The correct answer is D. All of the above.
Radio telescopes are better than optical telescopes because they can detect faint galaxies which no optical telescope can, they can work even in cloudy conditions, and they can work during the day and night.
Radio telescopes are able to detect faint galaxies because they are sensitive to radio waves, which are longer than visible light waves. This means that radio telescopes can see through dust and gas that would block visible light, allowing them to see objects that are too faint to be seen with optical telescopes.
Radio telescopes can also work in cloudy conditions because radio waves can pass through clouds. This is in contrast to optical telescopes, which can only see when the sky is clear.
Finally, radio telescopes can work during the day and night because radio waves are not affected by the Earth’s atmosphere. This is in contrast to optical telescopes, which can only see at night when the sky is dark.
As a result of these advantages, radio telescopes are often used to study objects that are too faint, too distant, or too obscured to be seen with optical telescopes. For example, radio telescopes have been used to study the early universe, to map the distribution of dark matter in the universe, and to detect black holes.