Some of my friends are interested in science, but none of them can tell ____________.
A lot of trees and flowers are on ______ of the river and the number of them is growing ______.
Old people must __________.
_Who is _____ English teacher, Lu Yu? _ Mr Tian teaches _______ English.
_ What ______ useful book! _ Is it _____ one that you borrowed from Mr Green yesterday?.
Which is right?