He has given me so much help that I really want to do something for him ______.

A．in turn

B．by turns

C．in return

D．in answer.

将甲、乙、丙三株大小相近的同种植物，分别进行不同处理，来探究影响侧芽生长的因素。实验结果如下图所示。据图判断下列说法正确的是

A．顶芽摘除后，侧芽生长停滞

B．甲侧芽生长快与生长素促进作用有关

C．细胞分裂素与侧芽的生长无关

D．甲为对照组，乙、丙为实验组