To set the thames on fire

This report <u><em>calls in question</em></u> all previous research on the subject.

To blow hot and cold

To cross swords

<u><em>Once in a while</em></u> he might gamble a little.

We should <u><em>do away with</em></u> the present examination system.

A fool's errand

Having sold off his factory, he is now a <u><em>gentleman at large</em></u>.

Tell me plainly who broke the mirror, <u><em>do not beat about the bush</em></u>.