量反应量效曲线的对数剂量图为:
A.直方双曲线B.对称S型曲线C.频数分布曲线D.直线E.累加量效曲线
参考答案:B
Mum ________ an English book for Dad yesterday. [ ]
A. buys
B. bought
C. buy
矿山建设的安全保障有哪些制度构成?