Which of the following is an autoimmune disorder?

Where are $H_{2}L_{2}$ molecules found in the body?

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.

After maturation,in primary lymphoid organs,the lymphocytes migrate for interaction with antigens to secondary lymphoid organs like:
$A.$ thymus $B.$ bone marrow $C.$ spleen $D.$ lymph nodes $E.$ Peyer's patches
Choose the correct answer from the options given below:

Lymphocytes are sensitive to .........

Match the Column-$I$ with Column-$II$ and select the correct option.

Column-$I$	Column-$II$
$1$. Cellular barrier	$A$. Saliva in the mouth
$2$. Physiological barrier	$B$. Interferons
$3$. Cytokine barrier	$C$. Natural killer (type of lymphocyte)
$4$. Physical barrier	$D$. Mucus coating of the respiratory tract