Assertion (A): Only a change in magnetic flux will maintain an induced current in a closed coil.

Reason (R) :The presence of large magnetic flux through a coil is maintains a current in the coil if the coil is continuous.

$EMF\text{'}e\text{'}=-\frac{d\varphi }{dt}$

So change in magnetic flux produce EMF  which in turn produce current provided circuit is closed

Therefore, EMF is produced by small change in flux also but a presence of flux without change will not produce EMF.