—Listen ! Helen is singing in the next room．

—It _______ be Helen．She has gone to Beijing．

A．can’t           B．mustn’t        C．may           D．should

——Listen! Helen is singing in the next room．

——It           be Helen．She has gone to Beijing．

A．can’t                   B．mustn’t                C．may                       D．should．

－Listen! Helen is singing in the next room.

－It ________ be Helen. She has gone to Beijing.

[　　]

—Listen！Helen is singing in the next room.
—It _____be Helen .She has gone to Beijing.