happened on the morning一句中ON對嗎

Preposition of time: (morning)

發生時間: ~ 單是 morning 一個字, 用 in the morning.
e.g. Phone him in the morning.

If you want to say that something happened in a particular morning (i.e. which morning), you use on.

He left after breakfast on Saturday morning.
On a fine January morning, Washington reviewed the troops.
On the morning of the 31st of October, he killed himself.
On the morning of our departure, an old man came up and spoke to him.
We met on a cold morning in early spring.

Regular events:
The museum may not open in the morning.
She goes to church on Sunday morning.

Exact time:
He wakes up at six o’clock in the morning.

如果是寫的是the morning(今早/任何一個早上)的preposition應該是on的，不過這句的是the morning of the 10th "day of this month"
留意the monring是被另一個preposition連住，這早上是附在of的日子(10號)上，所以句子的preposition並不是給"the morning"而是給10號這個特定日子

因此10th的正確prepsition是on "a day"

無論當中附加描述的是morning, afternoon或night/evening of那天都是用on入preposition.

不過正如我上文所寫，正規英文的日期是要加上"the" 10th的。

一個原則"凡涉及日子"的"在..."， 一律用on，看這裡更多。