单句改错,下面句子各有一处错误请找出并改正

题目

单句改错,下面句子各有一处错误请找出并改正
last month,they might stay at home
there may have some students playing in the class room
you needn't to sit here

答案

last month,they might stay at home　　　　　　stay-be
there may have some students playing in the class room have-be
you needn't to sit here 去年to