抽粪作业时，应保持（）。
A.场地清洁卫生，无遗洒粪便
B.无遗洒粪便
C.作业场地清洁卫生
D.工具干净
参考答案：A
周角=______度=______个平角=______个直角．
The l9th century ___ the greatest number of laws stopping the rights and progress of the black. [ ]
A. witnesses
B. is witnessing
C. witnessed
D. has witnessed
