When frozen carbon dioxide (CO2) is heated, it changes directly into a gas. Which statement BEST indicates that a physical change has taken place?
a. Heat caused an increase in gas production.
b. Heat caused a new substance to form.
c. Heat caused a decrease in energy.
d. Heat caused a change in state.

hello there the answer is d

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.