Why is progesterone production in the corpus luteum important in the first trimester of pregnancy?

a. to maintain the uterine lining
b. to provide nutrition to the embryo
c. to produce milk
d. to regulate the heartbeat of the fetus

a. To maintain the uterine lining

Explanation:

Progesterone is secreted by the cells of the corpus luteum. During the uterine cycle, it prepares the uterine endometrium for implantation. During the first trimester, progesterone maintains the uterine lining. Higher levels of progesterone inhibit the secretion of GnRH (gonadotropin-releasing hormone). This results in inhibition of the secretions of FSH and LH which in turn are required for the development of follicle and ovulation respectively.

Lower levels of progesterone during pregnancy results in sloughing off of uterine lining and the embryo during menstruation causing abortion.  

dna is made up of six smaller molecules -- a five carbon sugar called deoxyribose, a phosphate molecule and four different nitrogenous bases (adenine, thymine, cytosine and guanine).