Jack has been working hard and _____ is no doubt that he will do a good job in the entrance exam.
I was about to leave the office ______ an unexpected visitor came. A. while B. as C when D. before
It was a matter of ________ would take the position.
People try to avoid public transportation delays by using their own cars, and this ____ creates further problems.
After the new technique was introduced, the factory produced_____ cars in 2008 as the year before.
Great changes ______ in China in the past 20 years.