It suddenly occurred to him ____ he had left his keys in the office．

John feltwhen he heard theresult[ ]

I’m exhausted. I _____ on a project day and night.– You’d better have several days off after finishingit. Otherwise you might break down.

23. Don’t try to cheat the taxman(税务人员); you’ll never ______it.

Scientists have to work hard to keep ________ with modern discoveries and developments.