Find $\mathrm{A}$ and $\mathrm{B}$ in the figure

Spermiogenesis is possible due to....

In which of the following organism testes descends into scrotum in breeding season but in non-breeding season goes up

Sperm's acrosome has

Select the correct statement

$A$ : The first sign of growing foetus may be noticed by listening to the heart sound through the stethoscope.
$R$ : By the end of second month of pregnancy, the foetus develops limbs and digits.