fi you are not____by then ,i will take you to see a doctor用well 还是用better?为什么?

fi you are not____by then ,i will take you to see a doctor用well 还是用better?为什么?
fi you are not____by then ,i will take you to see a doctor
用well 还是用better?
为什么?

fi you are not____by then ,i will take you to see a doctor用well 还是用better?为什么?
better
因为后面的 by then ,存在比较的意思.
句子翻译过来就是：
如果你过一会没有好转,我就带你去看医生.