鉴别黄酮类化合物最常用的显色反应是
A．四氢硼钠反应 B．三氯化铝反应 C．三氯化铁反应D．盐酸-镁粉反应 E．二氯氧锆反应
参考答案：D
— Have you known Mrs. Jackson for a long time?
— Yes, since she _____ the music club. [ ]
A. has joined
B. joins
C. had joined
D. joined
无线调车灯显信号显示黄灯闪后绿灯长亮表示（）信号。
A、减速
B、加速
C、推进
D、溜放
