一定温度下，m g下列物质在足量的氧气中充分燃烧后，产物与足量的过氧化钠充分反应，过氧化钠增加了n g，且n＞m，符合此要求的物质是

①H₂　  ②CO　  ③CO和H₂的混合物　  ④HCOOCH₃      ⑤CH₃CHO

A．⑤

B．①②

C．①②③④

D．①②③④⑤

She is getting better by degrees, but it will be some time _____ she is completely well.

A．that

B．since

C．when

D．before