I've given the matter careful thought.

我对这件事认真考虑过了。

That matter requires careful thought.

这件事需要慎重考虑。

This problem calls for careful thought.

这个问题需要好好想一想。

Her suggestion requires careful thought.

她的建议需要慎重考虑。

The suggestion requires careful thought.

这建议需仔细思考。