老师发出信号后,孩子们都举起了他们的旗帜。

At a signal from their teacher, the children all held up their flags.

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At a signal from their teacher, the children all held up their flags.

signal 是名词,意思是"信号、标志",指用来传达特定信息的动作、声音或物体。在这个句子中,指老师发出的某种可见或可听的指示信号。

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