题目

.—When did you ________ to do the work?     —Two months ago, we are through 80% of it at the moment. A.    set off     B.set about     C.set up   D.set out 答案：D向盛有乙醇的烧杯中投入一小块金属钠，可以观察到的现象是 （   ）A．钠块沉在乙醇液面下面B．钠块熔成小球C．钠块在乙醇液面上游动D．钠块表面有气泡生成