英文句子纠错Some countries have single-sex education models,while

oth single sex and mixed schools co-exist是一个完整的主谓结构的句子,in others 是状语,不是主语,所以在others 后面不可以加have
both single sex and mixed schools co-exist这句话中,both single sex and mixed schools 是主语,co-exist是谓语动词,如果both 后面加了have,那就有两个谓语了,语法上也是不对的