--What do you think made Mary so upset ? ---______  her new bicycle.

Russia will soon return 174 sq km of territory on the northeast border to China．     more than 40 years of negotiations．

(2011·湖南高考)The ability ________ an idea is as important as the idea itself.

—I regret ________ you that your application has not been successful.—Not successful? I performed pretty well in my interview!

Many developed countries have agreed to help the less developed ones but it remains ________ whether they will take action or not.