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【单选题】
己知变量x和Y的协方差为-40，x的方差为320，Y的方差为20，其相关系数为（ ）。A.
0 5
B.
-0 5
C.
0 01
D.
-001
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举一反三
【单选题】The meeting held in our classroom yesterday _____ two hours. [ ]
A.
was lasted
B.
last
C.
lasted
D.
lasting
【单选题】The meeting lasted for ___.
A.
two hour and half
B.
two hours and a half
C.
two hours and half
D.
two and half hours
【单选题】预防产褥期泌尿系统感染的措施不包括（）
A.
待产时尽量排空膀胱
B.
大小便后及时清洁外阴
C.
每4～6小时更换会阴垫一次
D.
产后鼓励产妇多饮水
E.
产后至少每4小时排空膀胱一次
【单选题】We had a long meeting yesterday. It _____ four hours.
A.
kept
B.
spent
C.
continued
D.
lasted
【单选题】Yesterday we had a long meeting which four hours.
A.
kept
B.
spent
C.
continued
D.
Lasted
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