By the time I reached home, my parents _______the dinner for me already.[ ]

A. had cooked            

B. cooked

C. have cooked            

D. cook

前臂皮瓣的不足之处是

A．皮肤薄，不易塑形

B．按血管口径粗细，吻合成功率低

C．血管解剖不恒定，且要损伤局部感觉神经

D．皮瓣设计及切除较复杂

E．手术要牺牲一条前臂主干血管