要是游过河去，需要多少时间?

[误] How long would it take to swim through the river?

[正] How long would it take to swim across the river?

注：across 表示“到达一条线、一条河或一条道路的对面”(与“细而长”的物体相对而言的位置或动作)，through 不能用于从“细而长”的物体之一侧到另一侧的动作。