题目

—How long _______it _______ you to work out such a difficult problem? —About thirty minutes. A．did… take                  B．does… take                 C．did…cost 答案：A能把乙醇、乙酸、葡萄糖溶液用一种试剂区别开，这种试剂是（　　）A．新制氢氧化铜B．溴水C．银氨溶液D．酸性KMnO4溶液