The full form of $AIDS$ is:

Assertion $A$: For an $AIDS$ patient,it becomes impossible to protect against infections from various diseases.
Reason $R$: $HIV$ infection leads to a decrease in the number of helper $T$-lymphocytes in the body.
Which option is correct for Assertion $A$ and Reason $R$?

The $AIDS$ virus has:

Which virus directly attacks macrophages?

In the given flow chart,the replication of a retrovirus in a host cell is shown. Observe it carefully and fill in the blanks $A, B$,and $C$.

Which one of the following statements is correct with respect to $AIDS$?