你是校报英语版编辑Jack Smith，主要负责“你问我答”专栏，请就中学生李华的来信作答，给出适当建议。

Dear Mr. Smith,

    I'm a Senior 3 student. I have to take English exams every two weeks. But the results are always discouraging in spite of my great efforts. I don't know why. I 'm afraid something is wrong with my English learning method. What's worse, before each exam, I'm always feeling nervous and cannot sleep well. Could you give me some suggestions?

Li Hua

注意：

针对提出问题，给出信息完整的建议；

适当增加细节，以使行文连贯；

词数：100左右。开头与结尾已为你写好，不计入总词数。

Dear Li Hua,

    I've just got your letter and I know learning a foreign language can be challenging for some people.

……

Sincerely yours,

Jack Smith

His d____ made us realize that our life is easy to lose.

已知$\overrightarrow{a}$,$\overrightarrow{b}$均为单位向量，且$\overrightarrow{a}$$·$$\overrightarrow{b}$=0．若|$\overrightarrow{c}$-4$\overrightarrow{a}$|+|$\overrightarrow{c}$-3$\overrightarrow{b}$|=5，则|$\overrightarrow{c}$+$\overrightarrow{a}$|的取值范围是（　　）