题目内容
2. We observed some young men (slip) into the building at 23 : 00 last night.
2. slipping observe sb doing sth 看到某人正在做某事。
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题目内容
2. We observed some young men (slip) into the building at 23 : 00 last night.
2. slipping observe sb doing sth 看到某人正在做某事。