一送多受轨道电路受端电压的调整要均衡，最多相差不能超过（）V为合格。
A. 0.2
B. 0.4
C. 0.6
D. 1
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When is a first-hop redundancy protocol needed in the distribution layer？（）
A. when the design implements Layer 2 between the access arid distribution blocks
B. when multiple vendor devices need to be supported
C. when preempt tuning of the default gateway is needed
D. when a robust method of backing up the default gateway is needed
E. when the design implements Layer 2 between the access switch and the distribution blocks
F. when the design implements Layer 2 between the access and distribution block
急性左心衰竭病情发展极为迅速且危重，表现为突发严重呼吸困难，呼吸频率可达_______，端坐呼吸，频繁咳嗽，_________，有窒息感而极度烦躁不安、恐惧，面色灰白或发绀，大汗，皮肤湿冷。
清洁伤口一般在缝合后第3天换药1次，至伤口愈合或拆线时，再度换药。（）
A. 正确
B. 错误
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