“这条河流长度是那条的三倍”可以用两种比较结构表示：
1. A is + 倍数 + as + 形容词原级 + as B——表示“ A 是 B 的若干倍长”：
翻译 The river is three times as long as that one.
2. A is + 倍数-1 + 形容词比较级 + than B——表示“ A 比 B 长若干倍”：
翻译 The river is two times longer than that one.
但是,表示两倍的 two times 改成合音词 twice 更符合英语习惯——
The river is twice longer than that one.