单选题 A considerable amount of time and money has been invested in ______ this system.
A. defining B. implying C. reducing D. perfecting

【正确答案】 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 dance．(他们卖力地使舞蹈更加完美)。其他三项“defining定义；implying暗示；：reducing减少”都不正确。