He was able to follow the doctor's instructions on how to care for the patient.为什么要用on
问题描述：
He was able to follow the doctor's instructions on how to care for the patient.为什么要用on
他可以按着医生的指导来护理伤病员.
答
on 还有关于什么的意思...相当于about介词短语做后置定语修饰instructions？how to 是怎么去做...on how to care for the patient. 在句中这是什么成分捏？