在早上用in。在早上英文是In the morning。In the morning的例句I could have done without being woken up at three in the morning（其实用不着在凌晨三点钟就把我叫醒）。
In the morning的例句There was music and dancing till two in the morning（音乐和舞蹈一直持续到凌晨两点）；I want to make an early start in the morning（我想早上早点出发）。
