商业文书在写作时应注意哪些问题？
参考答案：
把握文书的风格，做好文书的布局，运用写作技巧。
简述通信系统的组成.
—What's the matter with you —After the long walk, my leg （）and I couldn't go any further.
A. gave out
B. gave off
C. gave in
D. gave up
