1. 介词across着重于“从一头或一边到另一头或另一边”，强调从表面穿过。如：

She went across the street to make some purchases.

2. 介词through着重于“穿越”，强调从一定的空间内穿过。如：

The sunlight was coming in through the window.

3. 介词over多表示从“上方越过”，如：

He failed to go over the mountain; he had to go round it.

4. 介词past表示从“面前经过”，如：

Someone has just gone past the window.