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【单选题】Obtaining Drinking Water from Air Humidity Not a plant to be seen，the desert ground is too dry．But the air contains water，and research scientists have found a (51) of obtaining drinking water from a...
A.
who
B.
where
C.
when
D.
which
【单选题】人工挖掘土方作业过程中，作业人员相互间必须保持足够的安全距离：前后作业，两人间距不小于(C)m;左右作业，两人间距不小于( )m。
A.
1;
B.
2;
C.
3;
D.
4;
E.
5;