国家三角测量规范规定，二等三角测量按三角形的闭合差计算的测角中误差不得超过（）。
A. 1″
B. 0.5″
C. 0.7″
D. 1.8&Prime
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可按照如下4种操作来区分控制流程的各种改变情况，即条件分支、（）、（）和过程返回。
As a network administrator, you are required to deploy MPLS technology. During the deployment, it is recommended to apply conditional label advertising. What is most probably the reason for that?（）
A. to enable label switching on the frame mode interface
B. to restrict MPLS availability to predefined time periods
C. to restrict end users from seeing the routers in the MPLS network
D. to restrict label switching to a limited number of network
缺油对变压器有（）等影响。
A. 造成瓦斯保护误动作
B. 绝缘损坏、击穿事故
C. 使线圈暴露则容易受潮
D. 使线圈绝缘下降
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