题目：\frac{2}{5}+\frac{2}{7}-\frac{2}{5}+\frac{2}{7}的结果是( ) 
选项：
bullet: A
text: \frac{2}{5}
bullet: B
text: 0
bullet: C
text: \frac{4}{7}
答案：C
解析：:\frac{2}{5}+\frac{2}{7}-\frac{2}{5}+\frac{2}{7}， =\frac{2}{5}-\frac{2}{5}+\frac{2}{7}+\frac{2}{7}， =\frac{2}{7}+\frac{2}{7}， =\frac{4}{7}. 故选:C.