The poor boy couldn't work the problem out. He wasn't ____ clever.

I ran across a car crash in Hong Kong, and ________, both sides just politely exchanged the telephone numbers and cards, a surprise to me.

–You are Mr. Zhang, aren’t you? --______. 

.—We’ll eat as soon as the meat is done.—It has__________to cook for another five minutes.

To be an astronaut, you must not only be strong in mind, but also be sound mentally and___.