An omnidirectional antenna is an antenna that radiates almost equal power in all directions in the horizontal plane, which is also called the azimuth plane1. This means that the antenna has a 360-degree coverage in the horizontal plane, but a narrow coverage in the vertical plane, which is also called the elevation plane2. An omnidirectional antenna is suitable for indoor environments where the clients are distributed around the access point3. Therefore, statement D accurately describes an omnidirectional antenna. Statements A, B, and C are incorrect because they describe different types of antennas. Statement A describes an isotropic antenna, which is a theoretical antenna that radiates equal power in all directions in both the horizontal and vertical planes. Statement B describes a vertical antenna, which is an antenna that radiates almost equal power in all directions in the vertical plane, but a narrow coverage in the horizontal plane. Statement C describes a directional antenna, which is an antenna that radiates more power in a specific angle and less power in others, creating a focused beam of radio waves. References: 1: Aruba Certified Network Technician (ACNT) Study Guide, page 872: Aruba Certified Network Technician (ACNT) Study Guide, page 883: Aruba Certified Network Technician (ACNT) Study Guide, page 89. : Aruba Certified Network Technician (ACNT) Study Guide, page 87. : Aruba Certified Network Technician (ACNT) Study Guide, page 88. : Aruba Certified Network Technician (ACNT) Study Guide, page 89.