MPLS is called Multi-Protocol Label Switching, which is correct about the label description in MPLS? (Multiple Choice)

MPLS is called Multi-Protocol Label Switching, which is correct about the label description in MPLS? (Multiple Choice)
A . MPLS system has a variety of label distribution protocols, such as LDP is a label distribution protocol
B . The label is carried by the header of the MPLS packet and has global significance, that is, the label value of all routers cannot be repeated
C . The label is a fixed-length identifier with only local significance, which is used to uniquely identify the FEC to which a packet belongs
D . MPLS supports single-layer labels as well as multi-layer labels

Answer: ACD