一种微风吊扇的叶片是由三块梯形的塑料片组成的，已知每块塑料片上底是3.2厘米，下底是4.5厘米，高是10厘米，做这个吊扇的三块叶片共需塑料片多少平方厘米？

Over a very large number of trials, the probability of an event ________ is equal to the probability that it will not occur.

A．occurring

B．to occur

C．occurs

D．occur