未经医师注册取得执业证书的（）

A.不得从事医师执业活动

B.可在预防机构从事医师执业活动

C.可在保健机构从事医师执业活动

D.可在执业医师指导下，在预防、保健机构，从事医师执业活动

E.可在执业医师指导下从事医师执业活动

To keep healthy, most retired people _______ jogging as a regular form of exercise.

A．take up

B．take on

C．give up

D．hold out