When people run long distances, their muscles require increased amounts of oxygen. Which system is responsible for carrying this oxygen to the muscles? Nervous

Respiratory

Digestive

Circulatory

the answer to this predicament is false, by friend, i had this on a quiz, and i got it wrong, so i learned it, cos i was gonna have it on a test, and i got it right

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.