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【单选题】
If there is an intruder _____the campus, students should be _____through an announcement, ______teachers should lock their classrooms to keep the children safe.A.
in, warned, after that
B.
at, warned, before which
C.
on, informed, after which
D.
in, informed, before which
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反馈参考答案：
举一反三
【单选题】设x=2,y=3,z=4,k=5,则表达式x
A.
1
B.
2
C.
3
D.
4
参考解析：
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