I'm studying for the N3 from Kanzen textbook and I came across this question
私は夏休みの( )、アメリカの友達の家にいた。
there are three choices: 間、間に、中で
the answer they consider it as the right one is 間. what was I thinking is that it might be interchangeable and both are correct because you are either spend the whole summer vacation at your friend's house or some time of the summer vacation? isn't it right?