请问补充250题69题

69.   The human growth hormone, made by the pituitary gland, is secreted during sleep in higher concentrations than when awake.

(A) during sleep in higher concentrations than when awake

(B) when sleeping in higher concentrations than waking hours

(C) in higher concentrations during sleeping than waking

(D) in higher concentrations during sleep than during waking hours（D）

(E) in higher concentrations when asleep than when awake

Key is D. But what's wrong with E?

Tks.

有道理。但是D中好像应该用during sleeping than during waking hours更对称，而用sleep不对称，是不是这样？

不是，这里是两个名词的平行，sleep 和 waking hours. 为什么要用动名词sleeping？

如果是sleeping hours, 形式上是平行了，但是不简洁。

谢谢