单项选择题 During many sectors are foundering, the $ 21 billion videogame-software industry is booming, adding game developers at a rate of 2,500 a year in the United States alone（）.

单项选择题 I can still vividly remember to pick our steps in the mountain down the deep valley on my 21st birthday（）.

单项选择题 I see four kinds of pressure working on college students today: economic pressure, parental pressure, peer pressure, but self-induced pressure（）.