all students are in the classroom nom 改为否定句

no students are in the classroom now.或者None of the students are in the classroom now
all students aren‘t in the classroom now 是错的，这是部分否定，意思是不是所有学生都在教室。

其实这道题目就是依据于肯定句直接变否定加上not就可以了。本句子含有be动词are。所以直接在are 后面加上not就可以了。

All the students are not in the classroom now.
或 Not all the students are in the classroom now. 这两句是不完全否定，意思：并不是所有的学生都在教室里。
None of the students are in the classroom now.这句是全否定，意思：所有的学生现在都不在教室里。

None of the students are in the classroom now

all students aren‘t in the classroom now

部分否定：Not all students are in the classroom.
全部否定：No students are in the classroom.
或 None of the students are in the classroom.