Jawaban:

(-) she's not returning a book to the library.

(?) is she returning a book to the library?

(-) they are not waiting for us.

(?) are they waiting for us?

(-) she's not finishing the math homework.

(?) is she finishing the math homework?

(-) they are not studying in the library.

(?) are they studying in the library?

(-) he's not having his lunch in the canteen.

(?) is he having his lunch in the canteen?

(-) they're not having a meeting in the teacher room.

(?) are they having a meeting in the teacher room?

(-) she's not meeting the principal.

(?) is she meeting the principal?

(-) they are not talking about the football match.

(?) are the talking about the football match?

(-) he is not buying something in the school co-op.

(?) is he buying something in the school co-op?

(-) we are not practicing English.

(?) are we practicing English?