What are antigens composed of?

Antibodies are synthesized by . . . . . . .

In an antibody,disulphide bonds are present . . . . . .
$i$. between two heavy chains
$ii$. between two light chains
$iii$. between the constant region of a light chain and the constant region of a heavy chain
$iv$. between antigen binding sites of both the heavy and light chains
$v$. between the variable region of a light chain and that of a heavy chain
Select the correct answer from the options given below.

$NK$ cells are which type of cells?

Which of the following is a primary lymphoid organ?

Which of the following statements is false?