What Conditions Restrict the Suitable Wavelength Range for Communication with Extraterrestrial

Multiple Choice

What conditions restrict the suitable wavelength range for communication with extraterrestrial intelligence to the "water hole" in the high-frequency radio range of the electromagnetic spectrum?

A) cosmic background radio noise at low frequencies and radio noise from the Sun and Jupiter at high frequencies
B) local radio noise from television, radio, and aircraft across the band, except a narrow range in which transmission is prohibited by international agreement to permit such extraterrestrial communication
C) atmospheric absorption by the ionosphere at low frequencies and by CO₂ at high frequencies in the long infrared range
D) high galactic radio background noise at low frequencies and high atmospheric absorption by H₂O and O₂ at high frequencies, with a suitable region in between