Refer to the exhibit. How many STP domains are present?

In a network running Per-VLAN Spanning Tree Plus (PVST+) or Rapid PVST+ (RPVST+), each VLAN creates its own independent STP instance, meaning three VLANs would result in three STP domains. Alternatively, the network could be segmented into three distinct Layer 2 broadcast domains, each with its own STP instance.

Without an exhibit, there is no inherent reason or common network configuration that would specifically result in four STP domains.

A single STP domain would typically indicate a single Layer 2 broadcast domain or a single Multiple Spanning Tree Protocol (MSTP) region encompassing the entire network.

Without an exhibit, there is no inherent reason or common network configuration that would specifically result in two STP domains.