第19题: [单项选择]Since the introduction of the new technique, the production cost ______ greatly. A. reduces B. is reduced C. is reducing D. has been reduced 参考答案:D 答案解析:[解析] 本题测试的是动词时态和语态的用法。由since引导从句或后跟名词,其主句要用现在完成时态。此外,cost是reduce的宾语。因此应用reduce的现在完成时而且要用被动语态。