Gmat Data Sufficiency

Gmat Data Sufficiency
"the range of the monthly closing balance"如何理解?
eg.Beginning in January of last year,Carl made deposits of USD120 into his account on th 15th of each month for several consecutive months and then made withdrawals of USD50 from the account on the 15th of each of the remaining months of last year.There were no other transactions in the account last year.if the closing balance of Carl;s account for May of last year was USD2600,what was the range of the monthly closing balances of Carl's account last year?
(1)Last year the closing balance of Carl's account for Apr was less than USD2625.
(2)Last year the closing balance of Carl's account for Jun was less than USD2675.
Answer:C
最好能翻译并给出中文详细解答.