What are $IgA$ and $IgM$?

What is injected to induce passive acquired immunity?

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.

Thymus is the site for the development and maturation of

Identify the correct group for primary lymphoid organs.

Match the following columns:

Column-$I$	Column-$II$
$1.$ Saliva and tears	$a.$ Cytokine barrier
$2.$ Mucus coating	$b.$ Cellular barrier
$3.$ $PMNL$	$c.$ Physiological barrier
$4.$ Interferons	$d.$ Physical barrier