If the number of throughs that pass a point in a given time increases, what has decreased

The number of throughs (and crests) that pass a point in a given time gives the frequency of the wave. In fact, the frequency is exactly defined as the number of complete cycles of a wave that pass a given point in a given time. Therefore, if the number of throughs that pass a point in a given time increases, the frequency of the wave increases as well. But the frequency is the reciprocal of the period:

where T is the period. The two quantities are inversely proportional to each other, therefore since the frequency has increased, the period of the wave has decreased.

Ibelieve the correct answer would be c.