英语求教,
12.All _____ is needed is a supply of oil.
A.the thing B.that C.what D.which
13.The foreign guests,_____ were scientists,were warmly welcomed at the airport.
A.most of whom B.most of them C.most of which D.most of those
14.On the train I saw a student _____ I thought was your sister.
A.who B.whom C.which D.that