—Listen! Is Mary singing in the next room?—No. It _______ be Mary．She has gone to Shanghai for an important meeting.

– Who didn’t turn off the light after school yesterday?– It ______ be Lucy. She told me she was the last one to leave the classroom.

—Look, someone left a book.—Oh, yeah … This book ________be Kitty’s. Only she likes to read this kind of books.

As we’re students, we __________ obey the school rules.

─ Is the woman in white our manager?  ─ It ________be her. She has just left for Shanghai.