题目

Large quantities of water ____ for irrigation.A. is needed     B. has needed   C. need  D. are needed 答案：D为提纯下列物质（括号内为杂质），所选试剂及方法均正确的是 选项        物质                                              除杂试剂                             方法 A              溴苯（溴）                                 CCl4                                       分液 B              硝基苯（NO2）                          NaOH溶液                          分液 C              乙烷（乙烯）                             氢气                                      洗气 D              乙酸乙酯（乙酸）                    NaOH溶液                          分液