第11题: [单项选择]Generating tubes in waste heat boilers are finned to (). A. reduce gas flow turbulence B. prevent exhaust gas corrosion C. increase the rate of combustion D. increase the rate of heat transfer 参考答案:D
第23题: [单项选择]--How did the boss pay the workers --As a rule, they were paid ______. A. by an hour B. by the hour C. by hour D. by hours 参考答案:B 答案解析:by可以用来构成短语作状语表示“按时间、长度、重量、数量等单位计算”的意思。但这个介词短语必须由by+带the的单数词形的有关名词构成,其中the含有“每一,每(per,each)”的意思。