She ________ hum pieces of music at the age of four. She is a talented singer. [ ]

A. can  

B. could  

C. must  

D. should

毛白杨接炮捻法育苗是（）和（）相结合的一种繁殖方法。

A、芽接

B、插条育苗

C、劈接

D、袋接