They are having a great time on the Great Wall.（同一句）
问题描述：
They are having a great time on the Great Wall.（同一句）
答
They are having fun on the Great Wall.
希望对你有帮助
答
They are enjoying themselves on the Great wall.
have a great time = enjoy oneself 过的很愉快
祝你学习进步,更上一层楼! (*^__^*)
不明白的再问哟,请及时采纳,多谢!