A．If the balance is below five hundred dollars．
B．If the interest rate varies．
C．If the customers open a new account．
D．If the customers want to check their account．

A．Play tennis．
B．Buy tickets for the tennis match．
C．Go for picnics．
D．Watch a tennis match．

A．Their favorite player will not turn up for the match．
B．The bad weather will affect the players' performance．
C．Their favorite player may be beaten down by his opponent．
D．The match will last for a long time．