【单选题】【消耗次数：1】
He has_______four interesting books.
①
wrote
②
written
③
been writing
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相关题目
【单选题】
She was wondering whether he has been writing anything new ____
①
late
②
later
③
latter
④
lately
【单选题】
Its ( ) that he has been away from home.
①
evident
②
important
③
genuine
④
alternative
【单选题】
he park has been built and it will be open _____ three years
①
A. in
②
B.for
③
C.on
④
D.after
【判断题】
Ever since he arrived, he has been complaining constantly about the weather.
①
正确
②
错误
【单选题】
He used to in a small village, but now he has been used to in the big city.
①
live, living
②
live, live
③
living, living
④
living, live.
【单选题】
A: Could you put the books on bookshelves, please? B: Of course. [填空] A: Thats all. Everything else has been done.
①
Its a pleasure to help.
②
Is that all?
③
Im free now.
④
How should I do it?
随机题目
【单选题】
高效液相色谱的主要部件包括
①
高压输液系统、分光系统、色谱分离系统、检测器
②
载气系统、进样系统、色谱分离系统、检测器
③
高压输液系统、原子化装置、色谱分离系统、检测器
④
高压输液系统、进样系统、色谱分离系统、检测器
【单选题】
以硅胶为吸附剂的柱色谱，分离极性较弱的物质时宜选用的流动相是
①
极性较强的流动相
②
活性较高的吸附剂和极性较弱的流动相
③
活性较低的吸附剂和极性较弱的流动相
④
活性较高的吸附剂和极性较高的流动相
【单选题】
采用吸附TLC法分离混合组分时，选择合适的分离系统(固定相与流动相)的目的在于
①
使Rf值在0.3～0.5范围内
②
分离开各组分且Rf值在0.2～0.8范围
③
减少拖尾
④
使斑点集中