from 的弱读

'From' is a preposition. It's usually not that important in a sentence, so it's often unstressed. At the end of a question it's still /frɒm/, but when it's unstressed and comes in the middle of a sentence, the vowel changes to schwa.

介词通常不是句子的重点，所以常常弱读。from 在句中时，中间的元音 /ɒ/（美式 /ʌ/）变成轻轻的 /ə/：I'm from London 读成 I'm frəm London。

例外是句尾：Where do you come from? 里 from 虽然也不重读，但后面没有别的词让它靠上去，所以元音保持完整。这条规律对大多数介词都适用：to、for、at、of 也是句中弱读、句尾读足。