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#}

—Where shall we meet tomorrow

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Pandas {#blank#}1{#/blank#} in our country.

We have decided to each sell five things {#blank#}1{#/blank#} we {#blank#}2{#/blank#} {#blank#}3{#/blank#} use.