I have some problems about how to use "in which, on which"
I will type the question,
July is the month ... the weather is usually the hottest
A. On which
B where
C. Which on
D. In which
D
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Sure.
Broadly speaking, we say
in a year
in a month
in a week
on a day
at a time, eg at 3pm.
This is all a bit idiomatic, and there are various exceptions to the above.
I think the underlying idea is this. If we are thinking of a period of time, we usually say 'in'.
Clive