Which statement about LDP session protection and ldp-igp sync is true:
A. both LDP feature can’t be used at the same time in MPLS LDP network
B. ldp-igp sync re-exchanges label info when a down-up event occurs, keep the adjacency info in down-up event
C. ldp section protection sync re-exchanges label info when a down-up event occurs, keep the adjacency info in down-up event
D. both ldp feature must be used together to increase fast convergence on mpls ldp network
