— Where is your ruler?— in the pencil caseA．They are B．It’s C．This is

问题补充：

— Where is your ruler?

— in the pencil case．

A．They are B．It’s C．This is

答案：

解析：本题的问句主语直尺为单数，回答语应该用it来代替直尺，故本题选B。