They need to study hard at school.(做两句否定句,两句一般疑问句）（一个是need动词用法,一个need的情态动词用法）
问题描述：
They need to study hard at school.(做两句否定句,两句一般疑问句）
（一个是need动词用法,一个need的情态动词用法）
答
否定句：They do not need to study hard at school,或者They need not study hard at school
Do they need to study hard at school?或者Need they study hard at school?
答
They don't need to study hard at school.
They needn't study hard at school.
Do they need to study hard at school?
Need they study hard at school?