I often spend half an hour (in) doing homework.in 可加可不加 一般不加 也可以说I often spend half an hour on homework.这是没有动词的做法。一般采取第一种。lz是预备年级吧。当然 第一句话也等于:It takes me half an hour to do my homework.it为形式主语,这两句话经常在改句中作为考点考你。很重要,lz要掌握啊、
I usually spend about half an hour doing my homework。
It usually takes me about half an hour to finish my homework.
二者选其一都可
保你正确,我是教英语的。
It usually takes me half an hour to do my homework
I usually do homework half an hour.