洪恩朗文3L看听学英语第二册 Lesson 91 How long’ve you been here?

Narrator: It’s midnight.
Two policemen are outside the
library.
1st Policeman: Look at that!
2nd Policeman: What?
1st Policeman: A light’s on in the library.
2nd Policeman: That’s funny.
The library’s shut.
1st Policeman: Let’s climb in and see.
2nd Policeman: Look!
There’s a man
in the reading-room.
1st Policeman: What are you doing here?
Professor: I’m reading.
2nd Policeman: But it’s midnight!
1st Policeman: How long’ve you been here?
Professor: I’ve been here
since this morning.
2nd Policeman: He’s been here
for fifteen hours!