请教一条有争议的GWD数学DS

Sue’s monthly earnings consist of a monthly salary and a 4 percent commission on the portion of her monthly sales that is in excess of $2,000.  If Sue’s monthly salary was the same in July as in August, how much greater were her sales in July than in August?

(1)     Sue’s monthly earnings were $3,620 in July and $3,580 in August.

(2)     Sue’s monthly salary was $3,500 in July and in August.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

这题的答案选A，可是有人也觉得应该选C，理由是首先必须得确定基本工资是大于还是等于3580，若大于3580，则很容易算出

若等于3580，其八月销售量应该是小于等于2000，从而无法算出其销售量差

同问 , 望达人告之

楼主说的有道理，但是应该确定基本工资是小于3580 还是等于3580吧