__________, they couldn’t make their head teacher change her mind.

A．Whatever hard they try

B．No matter how they tried hard

C．As they tried hard

D．Hard as they tried

普萘洛尔治疗心绞痛时可产生下列哪一种不利作用（）

A.心收缩力增加，心率减慢

B.心室容积增大，射血时间延长，增加氧耗

C.心室容积缩小，射血时间缩短，降低氧耗

D.扩张冠脉，增加心肌血供

E.扩张动脉，降低后负荷