She has a dog.it's hair _____ long 填什么,理由?

问题描述:

She has a dog.it's hair _____ long 填什么,理由?

it's hair _____ long (这题目有点问题,it's = it is 在这里不成立的啊!)
应该是:its hair (is) long.它的毛是长的.its是嘛意思?its = 它的