When the teacher came into the classroom, the students ____ in groups.

题型：单选题题类：模拟题难易度：普通

A、work B、have worked C、were working D、are working

举一反三

点拨：{#blank#}1{#/blank#}意为"当……时候"，后面通常接时间点，从句中谓语动词用短暂性动词。另外，while，意为"当……时候"，后面只能接一段时间，不能接时间点，其引导的从句的动作或状态往往与主句的动作同时发生。

While we were walking home, it began to rain.＝ {#blank#}2{#/blank#}

— No, I didn't. I ________ TV then.

—Sorry, Mum. I didn't watch the weather forecast just now. I________a football match.

He was{#blank#}1{#/blank#} {#blank#}2{#/blank#}his father at that time.

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