肛瘘挂线疗法最大的优点是
A．换药方便B．结扎线同时可作为瘘管引流物C．肛瘘复发率低D．不引起肛门失禁E．病人痛苦小
参考答案：D
—Why didn’t you go to yesterday’s meeting?
—I would have but I ______too busy working on the important experiment.
A．had been
B．was
C．were
D．am
种子植物输导有机养料的输导组织是（）
A.导管
B.管胞
C.筛管
D.伴胞
