水平安定面的作动机构是：（）。
A. 水平安定面PCU
B. 水平安定面蜗杆作动筒
C. 升降舵PCU
D. 方向舵作动筒
国家电网公司典型设计中，数据中心的ODS分为（）区。
A. 缓冲区、统一视图区
B. 缓冲区、逻辑区
C. 逻辑区、功能区
D. 统一视图区、逻辑区
两个液压马达两种速率控制决定水平安定面有几种偏转速度（）。
A. 二种
B. 四种
C. 六种
D. 八种
Which statement about vlan operation on cisco catalyst switches is true？（）
A. when a packet is received from an 802.1Q trunk，the vlan id can be determined from the source MAC address table
B. unkown unicast frames are retransmitted only to the ports that belong to the same vlan
C. ports between switches should be configured in access mode so that vlans can span across the ports
D. broadcast and multicast frames are retransmitted to ports that are configured on different vla
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