After studying in a medical college for five years, John _______ her job as a doctor in the countryside.

A．set out

B．took up

C．set up

D．set off

从一足足跟着地到该侧足跟再次着地为止所用的时间称为（）。

A、步长

B、步幅

C、步行周期

D、摆动相

E、支撑相