Oestrus cycle is cyclic changes in the activities of ovaries and accessory duct during

Explain the senescence phase.

$A$: No individual is immortal except one-celled organisms.
$R$: $A$ few number of plant and animal species have existed on Earth and do not die because of budding.

Select the incorrect pair :

Study the following statements and choose the correct option.
$I$. Life spans of organisms are correlated with sizes.
$II$. Death of all individuals is certain.
$III$. The organism's habitat,internal physiology,etc.,are collectively responsible for how it reproduces.
$IV$. When offspring is produced by a single parent with or without the involvement of gamete formation,it is called asexual reproduction.

Select the appropriate option regarding $Hydra$.