阀门阀体材质为球墨铸铁，涂（）用来识别。
A.黑色
B.银色
C.中灰色
D.天蓝色
参考答案：B
It is often________that one trouble never comes alone.In my rush to leave I forgot to take the
plan I had made the night before.[ ]
A. to say
B. saying
C. said
D. being said
库仑滴定法中，以电解碘化钾－溴化钾溶液所产生的（）进行滴定，根据电解所消耗的电量计算煤中全硫。
A、硫
B、钾
C、硫酸
D、碘和溴
