these days we have spent as much time as we---the national flower exhibition 能不能用could to prepacould to prepare 作状语？但答案是could preparing

these days we have spent as much time as we could preparing the national flower exhibition
as 。。。。。 as we could 是尽可能……的，这里修饰time
these days we have spent time preparing the national flower exhibition
spend on sth
spend (in) doing sth

不可以
as much time as we could可以先忽略，那么主句为we have spent time --- the national flower exhibition, spend的用法只有两种：1.spend time (in) doing sth. 2. spend time on sth.，故不可以用to prepare,但可以用on, 你可能要突出prepare,那只能是preparing了

这个题答案是有争议的,不过更多的人倾向于使用v-ing：
【These days时间状语】【 we】【 have spent】【 as much time宾语】 【as we could 状语从句】【preparing】the national flower exhibition
spend time doing sth
但是,其实用to prepare也有道理,因为符合句型结构——
do all/everything
as much as
what/whatever one can/could to do sth
意思是：
做某人所能够做的一切/尽可能多的/无论什么来做某事.后面用带to不定式做目的状语.
像这种有争议的题,一般只需要知道分析方法和所考知识点就行了,不必过多的花费心思,因为争论者各执一词,其实并没有实际意义.再说了,像这种问题说穿了就是【失误题】,正式高考中很罕见!
祝你开心如意!

答案是could to prepare才对吧...