This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Changes in the respiratory system in pregnancy: 
Select and explain. 
A. Vital capacity is increased, B. Subcostal angle remains unchanged, C. Tidal volume remains unaltered, D. Residual volume is decreased
D: Residual volume is decreased
Answer: D: Residual volume is decreased 
Explanation: Changes in respiratory system during pregnancy:

With the enlargement of the uterus, specially in the later months, there is elevation of the diaphragm by 4 cm.
Total lung capacity is reduced by 5% due to this elevation.
Breathing becomes diaphragmatic. Total pulmonary resistance is reduced due to progesterone effect.
The subcostal angle increases from 68° to 103°, the transverse diameter of the chest expands by 2 cm and the chest circumference increases by 5–7 cm.
 A state of hyperventilation occurs during pregnancy leading to increase in tidal volume and therefore respiratory minute volume by 40%.