The Olympic Games，________in 776 BC, did not include women players until 1912.

A．first playing

B．to be first played

C．first played

D．to be first playing

马铃薯软腐病的侵染来源主要是（），病菌也可在（）或（）中越冬，经（）或（）侵入，带菌率可达100%。