How many moons does Mars have?
Pro-sentence
In English, "yes", "no", "okay" and "amen" are common pro-sentences. In response to the question "Does Mars have two moons?", the sentence "Yes" can be understood to abbreviate "Mars has two moons."
Mars
Jonathan Swift made reference to the moons of Mars, about 150 years before their actual discovery by Asaph Hall, detailing reasonably accurate descriptions of their orbits, in the 19th chapter of his novel "Gulliver's Travels".