——This wall of air is an effective answer to the problem and it ____ work. ——But it is a question to put such a wall of air around the statue.
This machine, ______for many years, is still working perfectly.
This is the reason ______he didn't come to the meeting.
The way ______he looks at problems is wrong.
I can never forget the day _______ we worked together and the day ______ we spent together.
I have bought such a watch _______ was advertised on TV.