through,across,over 用法辨析

through 指“穿过门∕洞∕隧道∕人群∕树林” ；
Look! A train is going through the tunnel.(看，一列火车正穿过隧道)

across 和 over 都可指“跨过街道∕河流”，但表示“翻过”时只能用 over。
There is a bridge ove∕racross the river. （河上有座桥）

Please stop and look before you go across the road.（过马路前请停下来看看）
They climbed over the highest mountain in the world last month（.上周，他们翻越了世界上最高峰）