A.TCP retransmits
B.benign
C.greedy
D.drop sensitive
E.smooth
F.delay insensitive

A.Yes. Traffic can pass either from switch S6 to S3 to S2 to S1， or， from switch S6 to S5 to S2 to S1.
B.No. Traffic will pass from switch S6 to S5 and dead-end at interface Gi 0/0.
C.No. Traffic will loop back and forth between switch S5 and S2.
D.Yes. Traffic will pass from switch S6 to S3 to S2 to S1.
E.No. Traffic will either pass from switch S6 to S5 and dead-end， or traffic will pass from switch S6 to S3 to S2 and dead-end.