“是…的”句 the construction “是…的”

The construction “是…的”can be used to emphasize the time and location of past events, and the manner in which they have occurred. The word “是”is placed before the part to be emphasized （sometimes it can be omitted）, and the “的”is placed at the enc of the sentence. The negative form is “不是…的”。
Form:
Some sentences with a verb as the predicate simply express that a certain thing has happened in the past. The meaning of this kind of sentence is different from that of a sentence with “是…的” as predicate. Compare the following:
他是去年来的。 (emphasizes that the time when he came was last year)
去年他来了。（tells generally what happened last year）
The sentence with “是….的”can also be used to emphasize purpose, function, and origin, for example:
我今天是来文你问题的。
我是听朋友说的。