Which of these is a Layer 2 transport architecture that provides packet-based transmission optimized for data based on a dual （counter-rotating） ring topology？（）

A.FlexLinks
B.loop-free U
C.looped square
D.looped triangle
E.loop-free inverted U

A.0.01
B.0.1
C.1
D.2.5

A. activity audit
B. administration
C. policy establishment
D. technology implementation