Which statement is true about TCN propagation？（）
A. The originator of the TCN immediately floods this information through the network.
B. The TCN propagation is a two step process.
C. A TCN is generated and sent to the root bridge.
D. The root bridge must flood this information throughout the network.
Which is the summer load waterline on the load waterline mark?（）.
A. The first line at the bottom
B. The second line from the bottom
C. The third line from the bottom
D. The fourth line from the bottom
社会主义集体主义的道德要求的最基本的层次是（）。
A. 先己后人
B. 公私兼顾，不损公肥私
C. 先公后私，先人后己
D. 无私奉献，一心为公
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