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【单选题】
_____ the sun for too much time will do great harm to you. [ ]A.
Exposed to
B.
Being exposed to
C.
Exposing to
D.
To expose to
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【简答题】全回流时，操作线与（）重合，操作线方程为（），理论塔板数为（）。当回流比减少到（）称为最小回流比，所需的理论塔板数（）。适宜的回流比应通过（）确定。
【单选题】One of the most possible reasons for constructing the Dujiangyan Irrigation System is ( ) ?
A.
To solve the seasonal floods caused by the Minjiang River.
B.
To alleviate drought of the Chengdu city.
C.
To help people travel from west to the east.
D.
To facilitate transport of business materials.
【单选题】Dujiangyan is an irrigation system built in_______________________ by the Qin State.
A.
prehistoric period
B.
Warring States Period
C.
Shang Dynasty
D.
the Spring and Autumn Period
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