请教prep两道语法题目

Michael1983

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不太明白，为什么不用but，而用but are，前面的"are not...but"不是很好的平行结构嘛，但是根据答案却是"are not....but are"???

[upload=jpg]UploadFile/2007-6/20076288452717863.jpg[/upload]
为什么用that呢，这里应该指代的是carbon emissions吧，复数形式，应该用those啊？

applec

Q1. Structure X are not Y, ...., but are Z.

they = products.

carolinelmf

第一题我也不明白。第二题中that指level

applec

Q2:

If X is Y, Z will be K. (realistic/factual deduction)

If X was Y, Z would be K. (assumption only, not possible)

example: If I were you, I would marry her. (BUT I am NOT you, and I will always not be you)

If I heat the water, it will boil. (phyical fact)

That = level

comparing the level, not the emissions.

applec

Q1:

idiomatic:

X are not Y,favored because they (products of natural selections) enhance reproduction, but (X, well known) are Z.

will it be clearer?