“知之为知之，不知为不知，是知也。”对这句话理解较为准确的是（   ）   

增加：在缺词处加一个漏字符号（∧），并在此符号下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1）每处错误及其修改均仅限一词；

2）只允许修改10处，多者（从第11处起）不计分。

    I'm Li Hua , a student from FenDou Middle School, that has a history of 75 years. Lie in the west of ShanBa, it has seen great changes of this old town. I am proud to tell you that I studied hard since I came here. So far, under the help of my teachers and classmates I have learned lots of knowledges. Although I still have some trouble with maths at present, I won't lose my heart. I consider it not very difficulty to learn it well as long as I devote myself to learn it. I strong believe that I can be admitted by a key university.

下图是“1959年-2009年秦岭北坡某河流域平均月降水量及月径流深度变化”，可知该流域（    ）