单项选择题

What is the difference between 1+1 and 1：1 protection switching？（）

A. 1+1 is based on APS， while 1：1 is based on IPS.
B. 1：1 is used in SNCP switching， while 1+1 is used in MS-SPRing switching.
C. 1+1 sends signals on Working and Protect paths， while 1：1 sends signals only on Working path.
D. 1+1 sends signals on Working path ONLY， while 1：1 sends signals on both Working and Protect paths.

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