on a sunday morning ,it was a sunny day ,i was playing at the park.it was a sunny Sunday morning . I got to the park and played in it.你这个汉语句子似乎不完整。放心采纳,用in 是错误的。
On a fine(sunny) Sunday morning, I came to play in the park.
On a sunny on Sunday morning, I came to play in the park
In a sunny Sunday morning, I went to play at the park
i play in a park on a sunny Sunday.