There are two great belts or______ where ninety percent of all earthquakes take place; they may, however, happen anywhere at any time.

单项选择题As no two speakers of a language speak______, difference will be found in the pronunciation of the speakers.

单项选择题It is due to the invention of the computer that man has been able to work so many wonders in the past few years. A case ______is the successful launching of space shuttle.