21．This is just _____ challenging job all the students want to get. Do you have anyone in _____ mind for it?
A．a; the B．the; 不填 C．the; the D．a; 不填
22．— Please come in and feel free to take a look around the house.
— Well, big _____ it is, the furniture is too old.
A．while B．as C．how D．when
23．— Linda hasn’t shown up yet.
— It’s strange. She ________.
A．could B．might C．must have D．should have
