Assertion: Vigorous contraction of the uterus at the end of pregnancy causes expulsion.
Reason: The stimulatory reflex between the uterine contraction and oxytocin secretion results in weakening contractions.

Answer

C

Explanation

Vigorous contraction of the uterus at the end of pregnancy causes parturition. Parturition is induced by a complex neuroendocrine mechansim. The signals for parturition originate from the fully developed fetus and the placenta which induce mild uterine contractions called fetal ejection reflex. This triggers release of oxytocin from the maternal pitutiary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin. The stimulatory relfex between the uterine constraction and oxytocin secretion continues. resulting in stronger and stronger contractions.