A is an agent that can cause infections and diseases.

scientists ‍

Explanation:

Infectious diseases are caused by diverse living agents that replicate in their hosts

The agents that cause disease fall into five groups: viruses, bacteria, fungi, protozoa, and helminths (worms). ...

Infectious agents can grow in various body compartments, as shown schematically in Fig.

A Virus is an agent that can cause infections and diseases.

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.