It is often said that _______famers lead _______very hard but simple life.

A．/; /

B．/; a

C．the; /

D．the; a

反转录过程，最终合成的双链DNA长度比正链RNA（）

A.长度一样

B.稍长

C.稍短

D.结构相当

E.结构复杂