when I ran out to find that a big tree had fallen down 最前面的w

when后面要加时间状语,这里并没有提到,去掉后意为：我跑出去发现大树倒了
如果一定要加when可改为：When I ran out,I found out that a big tree had fallen dawn 意为：当我跑出去的时候,我发现大树倒了