Which of the following antenna types will be most effective as a near vertical incidence skywave (NVIS) antenna for short-skip communications on 40 meters during the day?

Near Vertical Incidence Skywave (NVIS) communication relies on directing radio waves almost straight up so they bounce off the ionosphere and return to Earth in a tight, local radius (usually 0 to 400 miles). This technique is excellent for regional, short-skip communications. To achieve this high-angle, overhead radiation pattern, a horizontal antenna must be mounted relatively close to the ground. Placing a horizontal dipole between 1/10 and 1/4 wavelength high causes ground reflections to combine constructively with the upward radiation, maximizing the signal directed straight up. If the antenna is raised to 1/2 wavelength, the overhead signal drops and the radiation angle lowers toward the horizon, which favors long-distance (DX) communication rather than NVIS. Vertical antennas are also poor choices for NVIS because they naturally have a low angle of radiation and a 'cone of silence' directly overhead.