Speaker A: It took me ten years to build up my business, and it almost killed me.

Speaker B: Well, you know what they say: ().

A. There is no smoke without fire.

B. Practice makes perfect.

C. All roads lead to Rome.

D. No pains, no gains.

欲鉴别一株高茎豌豆是否是纯合子，最简便易行的方法（）

A.杂交

B.回交

C.测交

D.自交