石棉尘埃对人体的哪一个器官有严重不良之影响?
A.胃
B.肺
C.肝
参考答案：B
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
防治土壤侵蚀的关键在于运用（）管理政策和科学实施治理措施。
A、土地
B、土壤
C、矿产
D、森林
