运动后即刻出现晕厥，原因可能是

A．体循环静脉回流减少

B．肺静脉回流减少

C．体循环动脉压下降，脑缺血

D．体循环静脉压下降，脑缺血

E．左心室搏出量减少出现窦性心动过速

Is it true ____________ the new drug takes effect, the child with cancer will have a slim chance of survival?

A．when

B．that

C．whenever

D．that when