实际上只有C这种结构,pass和past都有“经过”或者“过去”的意思,这两个字的发音比较接近,元音字母a都发短音,但是pass是一个动词,如：
Two score year have passed, but the rules remain unchanged.
past是一个形容词,或者介系词,表示“过去”或“经过”的意思,如：
The population of the world has grown fast in the past four hundred years.
When you read the past tense, which sound is last?
It is half past ten now.
希望我能帮助你解疑释惑.