Recycling is one way to protect the environment; reusing is _____.

—Is Mike a diligent student?  —No，but he is a lazy one，if   ___         ．

He told me only part of the story and that was ____.

What seems to be a simple idea always turns out _____ that is hard to put into practice．

—Mum, Where’s my______ shoe? I can’t______ it. —It’s under the desk.