B through表示“贯通、直穿、透过、穿过”的意思,即是从一头（边）贯穿到另一头（边）.例The river runs through our city.这条河流经我们市.He passed through the hall.他穿过大厅 across表示“横穿、横过、横渡、横跨” 例：I swam across the Changjiang River 20 years ago.20年前我横渡了长江.Look left and right before you go across the street.过马路时要左右看.
