Read the following passage and questions, then choose the right answer from options, the answer should be one of A, B, C, D.

<passage>:
It's my first go at delivering a baby by caesarean section – and the foetal head is impacted, jammed in its mother's pelvis. To be honest I'm struggling. but with a good outcome. Although the Tydeman tube is still in gestation, Desperate Debra herself is now thriving. To understand the desperation of Debra and how the Tydeman tube might help to relieve it requires a brief foray into basic obstetric knowhow.  Evolution has endowed us with heads proportionally so large that even when labour runs according to plan, the delivery process involves a bit of a squeeze. For the baby's head to get stuck on the way out may not be usual, but it's by no means a rarity. The standard response is to perform a caesarean section. Every year some 160,000 babies are born in the UK this way, with almost two thirds of them classified as emergencies. One audit has suggested that roughly 8,000 babies get stuck and have to be delivered by caesarean at a stage when their mothers are fully dilated. "Some of the babies will be so close to coming out by the normal route," says Tydeman, "that it's then difficult to get them back up and remove them through the hole in the woman's tummy." Which women are most at risk of this setback seems to be largely unpredictable. "We just observe that it happens… It's been discussed in the medical literature since the 1940s, but until 10 years ago, and throughout my training and most of my life as a consultant, it wasn't really talked about." Considering the universality of childbirth, impaction and the best way of dealing with it are topics that seem to have gone remarkably unstudied. "There are strong opinions about why it happens and what to do, but very little research evidence," says Tydeman, adding that many of these opinions are contradictory. In a protracted birth that's destined to end with a caesarean, the longer the labour is allowed to go on before the obstetrician decides to intervene, the greater the likelihood that the baby's head will become impacted. However, concern over the rising number of babies born by caesarean has made doctors more wary of doing them – one consequence of which is that medical staff may allow a difficult birth to continue for longer before they resort to surgery. This could be boosting the frequency of impaction. But, again, no one is certain. When obstetricians doing planned caesareans slice open a mother's womb, what they usually see is the baby's head. By slipping a hand round and below it they can easily guide the baby out. "When you do a caesarean for an impacted baby," says Tydeman, "you make the incision in the same place, but what you might come across is a shoulder because the baby's so much further down [the birth canal]." As I'd discovered for myself, sliding a hand around the baby's head is then far more difficult. "It makes your fingers hurt," says Tydeman. "It makes your pulse rate go up to about 200, and you break out in a sweat because know you've only got about five or 10 minutes before there are serious consequences. The clock is ticking." Tydeman can remember the exact moment when the idea of her having a greater role dawned on him. "I was on the sleeper train down from Scotland to London," he says. "Debra was with me because the first Tydeman tube had become available at St Thomas's… It was about midnight, I'd had my free whisky and I suddenly thought, 'Blow me! Even if the tube doesn't work, Debra could be useful as a teaching aid'." The following morning, at St Thomas's, Tydeman asked a visiting professor of obstetrics to have a look at Debra and tell him what she thought. She put her hand into Debra's womb, grasped the foetal head and said it felt just like the real thing. "Terribly flattering," Tydeman laughs. With a grant from the Guy's and St Thomas's Charity fund they made Debra more presentable. Tydeman showed the prototype to Adam Rouilly, an established company specialising in medical models and simulators. They were impressed. A year later, the first of Debra's smartened-up sisters was on the market. So how valuable in training medical staff is a simulator like this? Very, according to Annette Briley. Imagine it's the middle of the night and an unplanned emergency caesarean is required: "Some poor junior doctor might find himself trying to manage it on his own." To have practised the knack of extracting a firmly impacted baby from a simulator is lot better than first honing your skill on a real woman. It's still too soon to make a final judgement about Debra’s impact. "When we first brought Debra out," Briley recalls, "some of the really experienced professors said things like, 'We always managed without one. Why would you need this?' But ask them to have a go at using it and then they admit it's really good." Medicine as a whole has an oddly ambivalent relationship to innovation. Some new findings, techniques or equipment take years to penetrate the profession others are seized upon immediately. A proper study of the clinical effectiveness of the Tydeman tube will necessarily involve women giving birth. Assessing the value of Debra as a simulator didn't require human subjects and the team has already conducted such a study. Thirty obstetricians, from three NHS maternity units and with varying levels of experience, took part. They all received a brief explanation of how Debra works, and were then asked to try a timed removal of the foetal head at three different levels of difficulty. Overall, 87 per cent reported that the simulator offered a realistic experience of dealing with an impacted head, and 93 per cent thought it would be valuable as a training device. One of the treatments of choice in that era was, naturally, acupuncture. But how to teach tyro-acupuncturists where to place the needles? Simple. A life-size bronze statue dotted with small holes indicated the points of insertion. And how then to test the students' grasp of their subject? If the statute was hollow, filled with liquid and given an outer coating of wax to mask the holes, a correct needle insertion would be followed by a leak. Given the universality of childbirth it's no surprise that, then as now, the womb turns out to be the most simulated of our organs. For the benefit of 18th-century midwives and doctors-in-training, the Bologna surgeon Giovanni Antonio Galli devised a birthing simulator comprising a glass uterus supported by an artificial pelvis and containing a flexible foetus. Trainees had to deliver the baby while wearing a blindfold. Only the tutor could witness the fumbling of their hands. As the material for a convincing simulation, glass clearly has its drawbacks. But another 18th-century contraption used a pink cloth-covered mannequin comprising a female torso complete with genitalia, a set of implantable foetuses of various ages, and even – a real Oddly, as medicine became more scientific, most of these devices fell by the wayside. As an academic review of these and other devices has pointed out, much of the 20th century was something of Dark Ages for simulation. Its value in professional training has had to be rediscovered: an endeavour in which inventive people like Graham Tydeman, sometimes with workshops rich in discarded junk, are still fruitfully engaged. This article was originally published on TheLong+Short. Read the original article.

<question>:
Describe how the frequency of C-sections has changed over time

<options>:
A The frequency has gradually decreased
B The frequency has plateaued
C The frequency has no significant trend
D The frequency has steadily increased

<answer>:

D