下列不是水泵按照用途分类的是（）。
A、空调用循环水泵
B、卧式离心水泵
C、污水处理用水泵
D、农业用水泵
参考答案：B
It was only when I reread his poem recently _____ to appreciate its beauty.
A．that I began
B．did I begin
C．I began
D．until I began
120～160km/h区段接触线的坡度限界值不超过（）。
A、3‰
B、4‰
C、5‰
D、8‰
