________ students are in the classroom.

What’s the meaning of “by mistake?”—It’s “____”. [ ]

My father ___________ a letter yesterday, but I’m not sure if he has finished it. —Why not ask him about it ?

It’s wise to forget things which aren’t worth ______.

Mary, could you tell me if your mother _____ our school sports meeting tomorrow? –I think she will come to school if she _____ free.