题目

I regret _____ hard at school, or I would have succeeded in passing the exam. A. not to work    B. having not worked C. to have not worked   D. not having worked 答案：D 解析: regret doing sth.后悔做过某事；regret to do sth.遗憾（抱歉）地要做…向NaCl、NaOH、Na2CO3和Na2SO4四种溶液中，分别加入不同的物质，通过一步反应都能生成化合物M，则M是（ ）A．Ca（NO3）2B．NaNO3C．HNO3D．Ba（NO3）2