#### Answer

(b) decrease it

#### Work Step by Step

Capacitance(in air) $C=\frac{\varepsilon_{0}A}{d}$
From the above expression, we may say that the capacitance is directly proportional to the area and is inversely proportional to the distance between the plates. Therefore, if the area is reduced, the capacitance also gets reduced. In order to keep the capacitance constant, we need to increase it and this is possible if we decrease the distance between the plates.