Which two statements regarding to QoS marking are true? (Choose two)

Traffic shaping delays packets to conform to a configured rate but does not alter QoS marking fields in the packet header; remarking is performed by class-based marking actions, not by shaping.

Class-based marking is a two-step process: a classifier (using ACLs, NBAR, or match criteria) must first identify the traffic class, and only then can a policy-map marking action write the appropriate DSCP, CoS, or IP Precedence value into the packet header.

802.1Q/p CoS bits reside in the Layer 2 Ethernet frame header, while IP Precedence resides in the Layer 3 IP ToS byte; they are not both Layer 3 fields.

QoS marking establishes a trust boundary by assigning definitive priority values to packets at a controlled point in the network; scheduling mechanisms such as CBWFQ and LLQ read these marked values to determine forwarding order and bandwidth allocation.

DSCP is a Layer 3 field within the IP header's Differentiated Services byte, not a Layer 2 field; MPLS EXP (TC) bits reside in the MPLS label header, which is commonly referred to as Layer 2.5, not standard Layer 2.