The old couple, ____had been admitted to university, were living a hard life．

A．both their children

B．both of whom children

C．both of whose children

D．whose their children

学生在学习体操过程中，各种动作要素之间的协调性较差，常有多余动作，这是什么性质的问题（　）

A．动作幅度

B．动作结构

C．动作力量

D．动作速度