[单项选择]卫星通信和数字网络光缆就像高速公路一样，是促进社会经济发展的基础设施。它不仅包括地面光缆数字通信网络系统，而且还包括通信卫星、卫星定位系统和环境、灾害监测系统。此外，还有不断更新的社会、经济统计数据库和自然资源数据系列，以及宏观调控、规则决策和工程设计服务及知识库，逻辑推理机等人工专家系统，这样，才能有效地实现以信息交流代替人流、物流与能量流。
选出对“卫星通信和数字网络光缆”理解不正确的一项是( )
A. 它是指光缆数字通信网络系统
B. 它能促进以信息交流代替人流、物流和能量流
C. 它包含各种各样数据库系列和知识库系列
D. 它包括通信卫星、卫星定位系统和环境、灾害监测技术系统等

{{B}} Dangers of Using Computer Terminals{{/B}}
Undoubtedly, the computer has greatly increased human being’s working capacity and intellectual capacity, but it also poses dangers to its users.
The problems caused by the use of computers:
a. more frequent incidence of abnormity during (1) ______ (1) ______
b. increased stress and (2) ______to vision, worsening short, sight (2) ______
and an itching of the face. To solve this problem, one should take a rest from
time to time and place computers at a location where there is (3) ______ (3) ______
light and something else to look at.
c. constipation resulting from long periods of sedentary (4) ______ (4) ______
d. (5) ______due to crouching over an inconveniently positioned (5) ______
keyboard.
e. a sense of (6) ______owing to having puzzled over a