为什么用volunteer doctors而不用voluntary doctors?

volunteer和voluntaryvolunteer doctorvoluntary workvolunteer不是名词么,为什么后面可以加doctor,什么时候用volunteer,什么时候用voluntary 为什么用volunteer doctors而不用voluntary doctors? to be a volunteer is great还是being a volunteer is great 为什么不可以用to(不定式 谁知道为什么用doctor's? volunteer volunteer I think being a volunteer is helpful to people.为什么用 being请高手解答, 为什么志愿者工作用的是volunteer work而不是voluntary work? Where is your aunt?She is at the doctor‘s.为什么用doctor’s They aren't here now; they have gone to the _______(doctor). 为什么用doctor's? she had been at the doctor's for a long time为什么用doctor's I‘d like to be a volunteer.a volunteer为什么句子成分,表语还是宾语 博士为什么叫doctor Beijing 2008 volunteer用中文怎么讲 If I were a volunteer of Beijing Olympics是什么意思这是个演讲题目!为什么用were?那么该怎么写？ Did she see the doctor?为什么用did I have to see the doctor.为什么要用HAVE? Did she see the doctor?为什么用did急!