The actor ________ basketball regularly for some years when he was young.         [ ]

A. was playing  

B. played      

C. has played      

D. had played

达到形态成熟的种子具有的特点是：（）。

A．呼吸作用强

B．含水量高

C．种皮坚硬、致密，抗旱力强

D．种子不饱满