He told us that they would help us through the whole work.

很高兴为你解答.
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【解析】：

He told us that they would help us through the whole work.
他告诉我们在整个工作中,他们都会帮忙的.
这里的through the whole work 是作状语,这里through 是介词.
这里用 through 表示在整个工作的过程里,突出贯穿这个一个过程.
作用有点像during ,但是它强调“贯穿”这个过程.

祝开心~!