Answer:
Option A, The endometrium thickens in response to increased estrogen
Explanation:
During the proliferative phase of the menstrual cycle, the following events occurs
a) Development of follicles inside the ovaries
b) Follice mature for ovulation.
c) Levels of FSH increase
d) The uterus prepares itself for implantation.
The mature follice releases estrogen that causes the growth of glands along with thickening of endometrium thereby thickening the uterine lining
Hence, option A is correct