Answer: Option (D)
Explanation: A galaxy is considered to be a large and extensive body comprised of the interstellar dust particles, dark matter and variable gases. The above mentioned particles are attached with one another forming variable shapes and are all held by the gravitational force. Gravity is the main factor responsible for the existence of this galaxies.
This is the reason, why the different shaped galaxies exist in the vast space, maintaining some similarity with one another.
Thus the correct answer is Option (D).