The correct answer is A. Heliocentric theory
Explanation:
Galileo Galilei was an Italian astronomer, mainly known for his observations that led Galilei to conclude planets revolve around the Sun (Heliocentric theory) instead of the sun and other planets revolving around the Earth (Geogcentrict theory). One of the observations that make Galilei drew this conclusion were telescopic observation of Venus, in this Galieli noticed similar to the moon Venus had different "phases" or changed its size and lighting, which was only possible if the sun was in the center of the solar system and planets revolve around it including the Earth. Thus, that Galileo was Venus changing size proved the Heliocentric theory.
