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

<passage>:
their picket posts on the prison perimeter, a pilot and two bombardiers in each 'copter, stone-faced, staring grimly alert at the prison below. They were ready for the breakout. The rockets came back and roared harmlessly about, and went away again. They stayed away. The helicopter men never faltered and never relaxed. The prison below them was washed with light—from the guard posts on the walls, from the cell blocks themselves, from the mobile lights of the guard squadrons surrounding the walls. North of the prison, on the long, flat, damp developments of reclaimed guards in Estates-General Correctional Institution—better known to its inmates as the Jug—and if he hadn't been able to detect the scent of trouble brewing a cell-block away, he would never have survived to He demanded: "Why wouldn't you mop out your cell?" The girl lifted her head angrily and took a step forward. The block guard, Sodaro, growled warningly: "Watch it, auntie!" O'Leary shook his head. "Let her talk, Sodaro." It said in the Civil to a wrong start, but the question was, would putting her in the disciplinary block help straighten her out? He rubbed his ear and looked past her at the line of prisoners on the rap detail, waiting for him to judge their cases. the mess hall." He shook his head reprovingly at the prisoner. "The block guard had to break up a fight between her and another wench, and she claimed the same business—said she didn't understand when the noticed the captain coming by. Of course, there wasn't much to sweep—the spray machines and sweeperdozers had been over the cobblestones of the yard twice already that day. But it was an inmate's job to keep busy. And it was a guard captain's job to notice when they didn't. So why didn't this girl, this Sue-Ann Bradley, know hers? II Every prison has its Greensleeves—sometimes they are called by different names. Old Marquette called it "the canary " Louisiana State called it "the red hats " elsewhere it was called "the hole," "the it is a place for punishment. And punishment is what you get. Block O in Estates-General Correctional Institution was the disciplinary block, and because of the green straitjackets its inhabitants wore, it was called the Greensleeves. It was a community of irritable guard, climbing the steel steps toward Block O from the floor below, when she heard the yelling. "Owoo-o-o," screamed Sauer from one end of the cell block and "Yow-w-w!" shrieked Flock at the other. guard. The outside guard looked impassively back—after all, he was on the outside. The inside guard muttered: "Wipe rats! They're getting on my nerves." The outside guard shrugged. "Detail, halt knows I hate it when there's a woman in here. It gets the others all riled up." "Let them in," the inside guard told him. "The others are riled up already." Sue-Ann Bradley looked carefully at the floor and paid them no attention. The outside guard pulled the switch that turned on the tanglefoot electronic fields that swamped the floor of the block corridor and of each individual cell. While the fields were on, you could ignore the prisoners—they simply could not move fast enough, against the electronic drag of the field, to do any harm. But it was a rule that, even in Block O, you didn't leave the tangler fields on all the time—only when the cell doors had to be opened or a prisoner's restraining garment removed. on her face. It was her first experience of a tanglefoot field. It was like walking through molasses. The guard guffawed and lifted her up by one shoulder. "Take it easy, auntie. Come on, get in your cell." He steered her in the right direction and pointed to a greensleeved straitjacket on the cell cot. "Put that on. Being as you're a lady, we won't tie it up, but the rules laborers—"wipes," for short—or, at any rate, they had been once. They had spent so much time in prisons that it was sometimes hard even Sauer. You got me scared! I'm so scared, I'm gonna have to yell!" The howling started all over again. The inside guard finished putting the new prisoners away and turned off the tangler field once more. He licked his lips. "Say, you want to take a turn in here for a while?" "Shut up !" yelled the inside guard. III "I smell trouble," said O'Leary to the warden. "Trouble? Trouble?" Warden Schluckebier clutched his throat and his little round eyes looked terrified—as perhaps they should have. Warden afternoon, he was playing ball with the laundry orderlies in the yard." The warden, faintly relieved, faintly annoyed, scolded: "O'Leary, what did you want to worry me for? There's nothing wrong with playing ball in the yard. That's what recreation periods are for." Oh, curse the thing." His phone was ringing. The warden picked it up irritably. That was the trouble with those pale blue tablets, thought O'Leary they gave you a lift, but they put you on edge. "Hello," barked the warden, not even glancing at the viewscreen. "What Sue-Ann froze, waiting to see what would happen. What actually did happen was that the guard reached up and closed the switch that actuated the tangler fields on the floors of the cells. The prison rules were humanitarian, even for the dregs that inhabited the Greensleeves. Ten minutes out of every two hours, even the worst case lovely term for it. At the guard's yell, the inmates jumped to their feet. bed—nobody had warned her that the eddy currents in the tangler fields rubber the faster you tried to move, the greater the resistance. The guard peered genially into her cell. "You're okay, auntie." She proudly ignored him as he slogged deliberately away on his rounds. He didn't have to untie her and practically stand over her while asbestos-handled key held in a canvas glove. Flock was in that cell and he was doubled over. The guard looked at him doubtfully. It could be a trick, maybe. it had been made out of a bed-spring, ripped loose from its frame God knows how, hidden inside the greensleeved jacket God knows how—filed, and the blister against his abdomen, where the shiv had been hidden during other rest periods, felt like raw acid. "All right," whispered Flock, "just walk out the door and you won't get hurt. Unless the other screw makes trouble, you won't get hurt, so tell voice was a cheerful bray, though the serpent eyes were cold and hating. "Warden, you got to get a medic in here. My boy Flock, he hurt himself real bad and he needs a doctor." He gestured playfully at the guards with the shiv. "I tell you, Warden. I got this knife and I got your guards here. Enough said? So get a medic in here quick, you hear?" And he snapped the connection. O'Leary said: "Warden, I told you I smelled trouble!" operator: "Get me the governor—fast." Riot! The word spread out from the prison on seven-league boots. and stand right by the door and—" "Club!" snapped Alys, radarscope-sergeant, with two children querulously awake in her nursery at home. "What in God's name is the them out they were to fly interdicting missions at such-and-such levels on such-and-such flight circuits around the prison. and last of all, the helicopters took off ... and they were the ones who might actually accomplish something. They took up

<question>:
What are the tangler fields?

<options>:
A a type of uniform meant to keep the inmates secure
B electronic fields in Block O that identify inmates
C replacement for guards in Block O
D electronic fields near the floor to stop prisoners

<answer>:

D