Which of the following statements is true? only a few species have become extinct in the past 500 years. there have only been two mass extinctions in earth's history. the worst mass extinction was the most recent involving the dinosaurs. scientists believe human destruction of the environment is causing another mass extinction.

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.