[讨论]旧prep 77，as的问题

77.  

Scientists have found signs that moving water changed the chemical makeup of the surface of Mars in recent eras, therefore concluding that its crust is harboring up to three times as much water than was previously thought.

(A) eras, therefore concluding that its crust is harboring up to three times as much water than was

(B) eras, therefore concluding that the planet's crust harbors up to three times as much water or more as was

(C) eras and have therefore concluded that the planet's crust harbors up to three times as much water as

(D) eras and they have concluded, therefore, that its crust harbors up to three times as much water, or more, than 答案：C

(E) eras and concluded, therefore, that the planet's crust is harboring up to three times more water as was

答案怎么选出来的已经知道了，只是看着C项最后的as much water as 后面没有was感觉很别扭。我知道第二个as在这里当关系代词把water that省掉了，补出来并还原就应该是the planet's crust harbors water three times as much as water that was previously thought。如果没有was，比较对象不就变成了the planet's crust harbors water previously thought。这样读上去好像不通啊。

请牛牛指教！