<s>Human: 将一篇文章中的语法错误标记出来。
“John have been studying at this university for three years.”
</s><s>Assistant: “John have been studying at this university for three years.” 

应改为： 

“John has been studying at this university for three years.” 

错误在于主语John是第三人称单数，而动词却使用了复数形式have，应该改为has。
</s>