sb find it +adj to do sth中的it是形式宾语,adj.做了宾补,to do sth.是真正的宾语；而sb find it is +adj to do sth中it is +adj to do sth 整个是谓语动词find的宾语从句,其中,it形式主语；is系动词；adj.表语；to do sth.真正主语