15．This problem may lead to more serious ones if _____ unsolved.

　 　 A．making　　　　　　　　 B．left　　　　　　　　　　　 C．remained　 　　　　 D．keeping

14．---Where did you find the wallet?

　　 ---It was at the stadium ____ I played football.

　 A．that　　　　　　　　　　 B．where　　　　　　　　 C．which　　　　　　　　 D．there

13．This creature’s brain is small _____its body.

　 A．comparing to　　　 B．in relation to　　　　 C．concerning　　　　　 D．related to

12．Most people honestly admit that they hardly know a thing when it _____ understanding how a piece of music is made.

　 A．amounts to　　　　　 B．appeals to　　　　　　 C．contributes to　　　 D．comes to