第15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 dance.(他们卖力地使舞蹈更加完美)。其他
A. how to make a stone wall in New England B. why there are so many stone walls in New England C. which parts of New England first used stone walls D. why the fields in New England are so thin and rocky 参考答案:B