【请爱好英语的朋友帮忙分析句子成分,Examplefor:TheWTOcannotliveuptoitsname,ifitdoesn'tincludeacountrythatishometoonefifthofmankind.请问：“thatishometoonefifthofmankind.”是定语从句吗?为什么要】

　　请爱好英语的朋友帮忙分析句子成分,

　　Examplefor:

　　TheWTOcannotliveuptoitsname,ifitdoesn'tincludeacountrythatishometoonefifthofmankind.

　　请问：“thatishometoonefifthofmankind.”是定语从句吗?

　　为什么要用“is...to",是情态动词”tobe"形式吗?

　　如果把句子简化成这样可以吗：TheWTOcannotliveuptoitsname,ifitdoesn'tincludeacountrytoonefifthofmankind.

　　Thankyouverymuch!