What is the main lymphoid organ where all blood cells including lymphocytes are produced?

Which one is a mental disability

In the given flow diagram, the replication of retrovirus in a host is shown. Observe and answer the following questions.

$(a)$ Fill in $(A)$ and $(B)$

$(b)$ Why is the virus called retrovirus ?

$(c)$ Can the infected cell survive while viruses are being replicated and released ?

Which immunoglobulin is the largest in size