We all think it most foolish ________ such a mistake

The driver has much experience of driving, and _____ he behaved very calmly in the dangerous situation.

There is something wrong with my computer. ______, I can’t chat on the Internet now.

What’s this in English—It’s an _____.

Zetao easily proved himself to be a rising star with four gold medals during the 17th Asian Games, ______was held in Incheon, South Korea last year.