My father has _______ a worker for ten years. [ ]
A. be
B. being
C. is
D. been
答案:D
麻黄碱的鉴别反应()
A.碘化铋钾
B.碘-碘化钾
C.硅钨酸
D.二硫化碳-硫酸酮
E.铜络盐反应
电力机车重力的传递顺序是什么?