第2题: [单项选择]关于SDH特点不正确的是 A. 同步复用 B. 标准网络接口 C. 强大网络管理能力 D. 全网异步时钟 参考答案:D 答案解析:[命题目的] 考查SDH特点。 [解题要点] SDH全网共用一个时钟系统。 [错解分析] A)，B)，C)说法正确。 [考点链接] SDH克服了PDH许多缺点。
第28题: [单项选择]He began working with balloons______. A. as a relaxation from his work on aircraft B. as part of his job at the time C. as a hobby D. when he heard that some Americans had crossed the Atlantic in one 参考答案:C 答案解析:细节理解题 首先文中提到“Don Cameron's first job was at Bristol Aircraft，where he worked as an engineer．He then
