锅炉房屋顶不准用（）。
A.简易油毡屋顶
B.瓦楞铁
C.石棉板
D.以上都是
参考答案：A
Last year, I visited a chemical factory in Baise, there are about _____ workers in it. [ ]
A. six thousands
B. six thousand
C. six thousands of
D. six thousand of
溶液的浓度也是“五稳定”操作的内容
