Answer:
Correct answer is C. Irregular galaxies
Step-by-step explanation:
An irregular galaxy is a galaxy which does not have a well-defined structure and is not identical to an elliptical or a spiral galaxy. Irregular galaxies do not fall into any class of the galaxies having a distinct size and shape.
These galaxies are rich in dust and gas and do not have a smooth appearance. They appear rough and chaotic in structure when observed through a telescope. Furthermore, these are the type of galaxies which are still not fully understood by the astronauts.