Everyone should be careful of their behavior.哪里错了?
问题描述：
Everyone should be careful of their behavior.哪里错了?
答
behavior变成behaviors
behavior可数，他们的举止，所以要用复数。
答
Everyone should be careful of their behaviors
Everyone should be careful of his behavior
答
be careful about 当心,注意
答
没有错；
Everyone的谓语虽然要用单数，但后面的代词可用复数形式，所以their是对的；
behavior不可数，所以不加s也是对的。