单选题 In no circumstances can more work be got out of a machine than ______.
A. be put into it B. is put into it
C. to put into it D. that is to be put into it

【正确答案】 B
【答案解析】[解析] 本句的意思是“在任何情况下，一部机器所输入的功比对它输出的功多”。than is put into it是省略句．省略了主语what。