How to say - at morning(s) or in the morning (s)?

Question

i'm studying English, can't see the difference.

Also - at winter, summer (s) or in the winter (s), summer (s)

Thank you!

Answer 1

"In the morning." "In the winter."

Answer 2

in the morning..  during the summer mornings, during the winter mornings, never ''at'' in the morning...

Answer 3

in the morning

Answer 4

They usually aren't plural, that's just the way it is, no one can say why haha