题目选项分析

【细心！读到句尾最后一个词】【看到economic/economical就警醒起来】
① economic和economical
economic 是"经济上的"，economical是"节约的"。
② would have to 和have to在本题中两种含义都合理，因此没有必要做这样的区分。

economic 是"经济上的"，economical是"节约的"。

1. economic 经济学的
economical 节约的

注意最后一个词，economical是实惠的，economic是经济的

economical 节俭的

economic 是"经济上的"，economical是"节约的"
have to和would have to在这里没有什么区别

economical 和economic意思不一样啊兄弟！

1. To develop... = something needs to be done -> would have to [you would have to do x, to develop y]
2. Economic vs. Economical: economical refers to "thrifty, efficient"; economic refers to "monetary considerations

economic 是"经济上的"，economical是"节约的"。

词语意思改变了:
"economic" means "having to do with "economics and/or the economy". (this is the intended meaning.)
"economical" means "efficient" or "at low cost/expense". (this is not the intended meaning.)因为句子对比前后的动词不一样，所以不可以省略they do.
RON:the verb that you're trying to omit is not exactly the same as its counterpart.
specifically, the first verb is in a hypothetical/conditional tense (would have to know...), while the second verb is in the present tense (they do [= know] now). you are not allowed to imply such tense transitions.
if you omit the verb, the omitted verb will be assumed to be in the same tense as its parallel counterpart. since you have to change tenses in this problem, you must include both verbs.