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#}

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Mike and Jane {#blank#}1{#/blank#} {#blank#}2{#/blank#} last year.

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One of the {#blank#}1{#/blank#}  {#blank#}2{#/blank#} {#blank#}3{#/blank#}  {#blank#}4{#/blank#}happened in October{#blank#}5{#/blank#} in April.

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