Refer to the exhibit. Which command or set of commands configures switch B as the primary root for VLANs 10, 15, and 20?

`instance 1 vlan 10,20` is used for mapping VLANs to an MST instance, not for configuring the root bridge priority.

`spanning-tree vlan 10,20 root primary` is a command used in Per-VLAN Spanning Tree Plus (PVST+) or Rapid PVST+ (RPVST+), not Multiple Spanning Tree (MST), to set the root for individual VLANs.

`interface range g0/0/0-15` is a command to enter interface range configuration mode, which is irrelevant for configuring the root bridge priority for an MST instance.

The command `spanning-tree mst 1 root primary` configures Switch B to become the primary root bridge for MST instance 1. MST instances map multiple VLANs to a single spanning tree instance, allowing efficient management of STP for groups of VLANs. If VLANs 10, 15, and 20 are mapped to MST instance 1, this command correctly makes Switch B the root for those VLANs by setting its priority to a lower value than other switches.