A nurse instructs a prenatal class about the importance of doing Kegel exercises frequently. Kegel exercises help to

A. promote better breathing by strengthening the diaphragm muscle.
B. maintain good perineal muscle tone by tightening the pubococcygeus muscle.
C. minimize leg cramps by strengthening the calf muscles.
D. prepare the mother for pushing by strengthening the abdominal muscles.

据报道，新中国成立60周年，将举行首都阅兵。这次阅兵将涉及陆、海、空、二炮各军兵种部队。以下对新中国成立60周年以来国防建设表述不正确的是[ ]

A．人民空军已发展成多兵种部队，成为共和国的“空中保护伞”

B．导弹部队已形成近、中、远程和洲际导弹的装备系列

C．实现了以空军为主体的向陆海空等诸多兵种合成转变

D．人民海军先后建立了东海、南海和北海舰队