她拒绝花超过30美元买一双鞋。

She refuses to spend more than $30 ___on a pair of shoes.

我已经在这上面浪费了太多时间。

I've wasted too much time ___on this already.

我喜欢它，并且我所有的时间都花在它上面。

I love it and I spend all my time ___on it.