What class are they having—Math. Their math teacher is _____ the classroom.

While typing, Helen has a habit of stopping ______ to give her long and flowing hair a smooth

Ladies and gentlemen, please ______ seated until the plane has come to a complete stop.

People were perhaps more honest a long time ago when life was very different from _________ it is today

当你称呼李老师（男）时，应如何称呼________.