第19题: [单项选择]A considerable amount of time and money has been invested in______this system. A. defining B. implying C. reducing D. perfecting 参考答案:D 答案解析:[解析] 本题空格处是说完善这个系统。D项的perfecting“完善”符合题意,如:They worked hard to perfect their deice.(他们努力地使舞蹈更加完美。)其他