【定语从句题1.Istheriver__that___flowsthroughthetownverylong?Isthiscollege__theone____thewenttolastyear?请问这两个句子有什么区别为什么一个用that一个用theone?theone和that在定语从句里的区别是什】

　　定语从句题

　　1.Istheriver__that___flowsthroughthetownverylong?

　　Isthiscollege__theone____thewenttolastyear?

　　请问这两个句子有什么区别为什么一个用that一个用theone?

　　theone和that在定语从句里的区别是什么?

　　2.Whendeeplyabsorbedinwork,______which___heoftenwas,hewouldforgetallabouteatingorsleeping.

　　请问这个是不是作表语?为什么要用which?