求解！！！一道Prep上的DS题

FGHYU19912301

Beth's bank charges a service fee on a regular checking account for each month in which the balance on the account falls below $100 at any time during the month. Did the bank charge a service fee on Beth's regular checking account last month?
(1) During last month, a total of $1,000 was withdrawn from Beth's regular checking account.
(2) At the beginning of last month, Beth's regular checking account balance was $500.

答案：E
为什么？想不通...结合2个条件已经远远低于100了，为什么还不能确定是否charge a service fee？
谢谢

soojin3215

因为 没有考虑到他有没有在这个月里往里放钱
应该整个的fall= 起初的-withdrawn+往里放的 如果这个是负的 且小于100 才会要 service fee

我觉得应该是这样的。。