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
网友回答
A. in, warned, after that
B. at, warned, before which
(答案→)C. on, informed, after which
D. in, informed, before which
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