请问My job is only to look after the children.这个句子中的动词不定式作什么成份理解比较好?另外请问My only hope is to continue my study.这一句里动词不定式充当的成份也是和上述句子一样吗？还有You are to finish it by six.这样的句子里的动词不定式呢？

请问My job is only to look after the children.这个句子中的动词不定式作什么成份理解比较好?
另外请问My only hope is to continue my study.这一句里动词不定式充当的成份也是和上述句子一样吗？还有You are to finish it by six.这样的句子里的动词不定式呢？