以下是一段听力
M :Hey，Helen， how are you？
w：i am fine ，Bob
M Are you going to the Rock concert tonight？
w：i haven't thought much about it.Are you？
M:sure，would you like to go with me？
W:sounds like fun
M YOU‘d have to buy your own ticket
w are you broke again？let me treat you
M wow！when did you come into so much cash？
w：you know i got a part-time job at the student center
m：since you’ve been so great about buying the tickets，why don't i take you out to dinner
问题：why is Helen buying the tickets？
a bob doesn't seem to have much money
b bob treated her last time
请解释？

当然是选A，因为材料中说w are you broke again？let me treat you