参考答案：A

解析：[听力原文]
Why did the chairman’s wife treat the student that way

短文中提到“How could this black-skinned girl score higher on the test than other students ”和“…At North Carolina College，color was used in deciding status…they Were always a bit surprised when a dark-skinned student did well，especially if she was a girl．”由此可以判断，A项“因为她是一个黑人”是正确的选择。