In the past ,all of the buses were double-decker ones.(改成否定句)

否定句 In the past , none of the buses were double-decker ones.

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In the past ,all of the buses weren't double-decker ones.

In the past ,all of the buses were not double-decker ones
在系动词后加not, 因为有all , 为部分否定

全部否定为：

In the past ,none of the buses were double-decker ones



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