Which of the following are the most abundant types of antibodies?

Assertion $(A)$: The human body is exposed to a large number of infectious agents daily,yet only a few result in disease. Reason $(R)$: The human body possesses an immune system. Which option is correct for Assertion $(A)$ and Reason $(R)$?

$A$ person who met with a road accident is likely to develop tetanus. He is immunized by administering:

Antibodies are synthesized by . . . . . . .

In the given figure,what does the part labeled '$A$' represent?

Which of the following is a primary lymphoid organ?