问题
单项选择题
Erosion that is a slow process, but it constantly changes the features on the surface of the earth.
A．which is
B．although
C．being
D．is
答案
参考答案：D
解析：结构应用。本句是由but连接的并列结构，前后均应有完整的主谓结构；划线部分中的that使前句成为一个从句，去掉它则句子成立，因此D为答案。