Except skin, other physical barriers which also helps to prevent the entry of the microorganisms are

$I.$ mucus coating of the epithelium lining the respiratory

$II.$ gastrointestinal tracts

$III.$ urogenital tracts

Choose the correct option

$A$ : Antibiotics like penicillin can be used to treat common cold.
$R$ : Penicillin causes lysis of viral cells.

AIDS is characterised by a sharp reduction is

When children play bare footed in pools of dirty water and flood water, they may suffer from diseases like

‘Black death' is related with