1) in
2) at
3) on
Объяснение:
1) in winter
2) at 3 o'clock
3) on 6, January
Объяснение:
"in" - ispolzuyem pered nazvaniyami vremen god;
"at" - ispolzuyem kogda govorim o vremeni = skolko chasov;
"on" - ispolzuyem pered datoy i dnami nedelami (on 19th December; on Monday).