如何区分walk past walk along和walk straight

如何区分walk past walk along和walk straight

walk past 经过，路过
walk along沿着……往前走
walk straight一直往前走

例如：
I heard Lucy singing when I walked past the classroom yesterday.
昨天我经过教室的时候听见露丝正在唱歌。
Walk along this road and take the second turning on the right.
沿着这条路往前走，在第二个拐弯处向右拐。
Walk straight on ,and you'll see the post office on the left.
一直往前走，你会发现邮局就在你的左边。