泛指和特指的区别。in summer就是一般的在夏天里，没有特别说明是今年的夏天还是过去的夏天，是泛指，例如：We like swimming in summer.而in the summer是特指某一个夏天，例如：in the summer of 1996。
summer相关例句I haven't seen him since the summer before last.
我已有两个夏天没见过他了。
Each summer a new batch of students tries to find work.
每年夏天都有一批新的学生要找工作。
I made painting the house my project for the summer.
把房子粉刷了一遍，这就是我的夏季工程。
in summer例句Even in summer this place did not look exactly hospitable.
即使在夏天，这个地方看起来也不太舒适宜人。
Food is apt to deteriorate in summer.
食物在夏天爱变质。
What time does it get dark in summer?
夏天什么时候天黑？
in the summer例句Why don't you come over to England in the summer?
你为何不在夏天来英格兰呢？
Anna sat her finals in the summer.
安娜在夏天参加了课程终结考试。
They plan to get married in the summer.
他们打算夏天结婚。
