517.So far we have done a lot to build a low-carbon economy,but it is _______ ideal.We have to work still harder.

A.next to

B.far from

C.out of

D.due to

518.We give dogs time,space and love we can spare,and ________,dogs give us their all.

A.in all

B.in fact

C.in short

D.in return

517.答案是B;

far from远非；next to仅次于；due to因为，由于。根据句意，我们所做的离理想中的要求还差很远，仍需努力。

518.答案是D;

in all 总计，总之；in fact 事实上；in short 简而言之；in return 作为回报。