[求助]GWD1－32

Q32:

To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.

No, the answer ought to be D. It is wrong to dispense with "they do", a ellipsis or a omission which would ruin the comparation. Besides, economic is more suitable for the logical sense of this sentence.

那么说是答案给错了？

可为什么economic在这里优于economical啊？

另外，would一定要补出的吗？我觉得不加would挺好啊。

would 给不给出，我倒觉得不是关键，

ETS在有些语法点上很灵活：比如gemj曾提到

好比说ETS喜欢平行结构，对应的它必然给你来一个形式上不平行的正确选项（太多了，举不胜举）。最恶毒的是这个：
396. In recent years cattle breeders have increasingly used crossbreeding, in part that their steers should acquire certain characteristics and partly because crossbreeding is said to provide hybrid vigor.
(A) in part that their steers should acquire certain characteristics
(B) in part for the acquisition of certain characteristics in their steers
(C) partly because of their steers acquiring certain characteristics
(D) partly because certain characteristics should be acquired by their steers（E）
(E) partly to acquire certain characteristics in their steers
另外：
require of sb to do sth
一会儿是对的，一会儿是错的。
cost of... to
也是一会儿是对的，一会儿是错的。
比较的助动词一会儿省略，一会儿不省。
考试时，这根弦一定要绷紧啊！要掌握ETS改错的精髓，并灵活运用。

MM不妨查查economic和economical的意思区别，这里的意思是the social and economic determinants 社会和经济（不是便宜）因素

那么这一题的突破点是不是economic和economical，和助动词的补出啊？

再次感谢bon gg的耐心回答！

偶喜欢用排除法

就是先economic和economical

再看有没有they do

是啊是啊，有谁能解释解释？