这个谜语很巧妙，你能猜出答案吗？

This riddle is very ___clever. Can you guess the answer?

那是个节约能源的巧妙主意。

That's a ___clever idea for saving energy.

我有一个开罐子的巧妙小工具。

I've got a ___clever little gadget for opening jars.