We can see a candle flame at 30 miles on a clear, dark night, and we can hear the tick of a watch 20 feet away in a quiet room. These two facts are examples of .

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.

d we did this already

the answer is d p: cell, q: organ, r: organ system, s: tissue