光纤的纤芯完成光信号的传输，光纤的包层负责将光封闭在纤芯内并保护纤芯，增强光纤的强度。
参考答案：对
Which of the following statements best describes humor in China
A．It is more or less the same in all parts of the country.
B．It is drastically different in every part of the country.
C．It is distinguished from Hong Kong.
D．It is more a verbal act than a physical act in the north.
建设过程项目进度控制在管理观念方面存在的主要问题是( )。
A．认为进度计划应体现计划系统的观念
B．不进行进度计划的优化
C．要在多个方案上充分比较，进行优选
D．缺乏动态控制的观念
