His first novel was _       , and he hasn't written anything decent since.    [ ]

A. a flash in the pan    

B. the flash in the pan    

C. in a flash          

D. like a flash

（）及自交系发生变异是玉米自交系混杂退化的原因。

A、生物学混杂和植物学混杂

B、机械混杂和生物学混杂

C、植物学混杂和动物学混杂

D、生物学混杂和动物学混杂