[tex]\huge{\boxed{\text{January}}}[/tex]
A counterexample is an example that proves the statement wrong.
In this case, we are trying to prove that not all months that start with J are summer months. This means we need to find a month that starts with J that is also not a summer month.
[tex]\boxed{January}[/tex] is the only month that fits this criteria. It begins with the letter J and is a winter month, which is not summer.
