Why Are Microwave Antennas Characterized by High Gain and High

Why are microwave antennas characterized by high gain and high directivity?

A) because there is no need for omnidirectional antennas since all microwave links are point-to-point
B) microwave transmitters are very limited in their output power
C) since device noise is greater at these frequencies, receivers require larger input signals.
D) because of the short wavelengths involved, the physical sizes required are enough for designs not practical at lower frequencies.
E) all of the above