In a circuit,the current lags behind the voltage by a phase difference of $\pi / 2$. The circuit contains which of the following?

Match the columns.

Column-$I$	Column-$II$
$(a)$ Parturition	$(p)$ Attachment of embryo to endometrium
$(b)$ Gestation	$(q)$ Release of egg from Graafian follicle
$(c)$ Ovulation	$(r)$ Delivery of Foetus from uterus
$(d)$ Implantation	$(s)$ Duration between pregnancy and birth
	$(t)$ Formation of zygote by fusion of egg and sperm

$A$ ball of mass $m$ and radius $r$ is gently released in a viscous liquid. The mass of the liquid displaced by it is $m'$ such that $m > m'$. The terminal velocity is proportional to

If $x > 0, y > 0, z > 0, xy + yz + zx < 1$ and if $\tan^{-1} x + \tan^{-1} y + \tan^{-1} z = \pi$,then $x + y + z$ equals to

If $x \log x \frac{dy}{dx} + y = \log x^2$ and $y(e) = 0$, then $y(e^2) = $

In tissue culture experiments,leaf mesophyll cells are put in a culture medium to form callus. This phenomenon may be called as: