Antibodies are produced when the body is exposed to
a. white blood cells.
b. receptor proteins.
c. antigens.
d. macrophages.

Antibodies are produced when the body is exposed to antigens.

During an initial encounter with a foreign antigen, the body's immune system namely the adaptive arm of the immune system, produces memory cells, a group of special lymphocytes that retain and store memory of the antigen.

On a second encounter with the same kind of antigen, the immune system "remembers" the antigen and mounts a rapid, specific and vigorous immune response against the antigen. This response includes the production of massive amounts of antibodies very specific to the antigen.

The antibodies effectively neutralize the antigen and facilitate its destruction.

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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.