Trunk interfaces can send both tagged and untagged frames.

The statement is correct. An IEEE 802.1Q trunk interface is designed to carry traffic for multiple VLANs. It accomplishes this by adding a VLAN tag to frames for most VLANs. However, one VLAN is designated as the native VLAN (or the VLAN corresponding to the Port VLAN ID - PVID). Frames belonging to this native VLAN are transmitted across the trunk link without a VLAN tag (i.e., untagged). Therefore, a trunk interface is capable of sending both tagged frames (for non-native VLANs) and untagged frames (for the native VLAN).

B. False: This option is incorrect. The ability to handle one untagged VLAN is a standard and essential feature of 802.1Q trunking, used for backward compatibility and for certain types of control plane traffic.

1. Huawei S5700 Series Switches Product Documentation, VLAN Configuration Guide - Fundamentals of VLAN, Section "Port-Based VLAN". The documentation describes a trunk port: "A trunk port allows packets from multiple VLANs to pass through. Except for packets from the default VLAN, packets passing through a trunk port are tagged." This confirms it handles both.

2. IEEE Std 802.1Q-2018, IEEE Standard for Local and metropolitan area networks--Bridges and Bridged Networks. Section 6.7, "Port VLAN ID (PVID)," describes the identifier for the VLAN to which untagged frames received on a port are to be associated, which is fundamental to how trunk ports handle untagged traffic.