Final answer:
The correct terms to complete the sentences are binary for two stars in a system, open for star clusters with up to a few thousand stars, and elliptical for massive galaxy systems with over a million stars.
Thus, the correct option is A.
Step-by-step explanation:
The correct words to complete the sentences with respect to star systems and galaxies are as follows:
- A) A binary star system is made of two stars.
- B) An open star system is made of no more than a few thousand stars.
- C) An elliptical galaxy is made up of more than a million stars.
Binary star systems, like our own solar system's nearest neighbor, Alpha Centauri, consist of two stars that orbit a common center of mass. Open star clusters, such as the Pleiades, contain a relatively small number of stars bound by mutual gravitational attraction. Lastly, elliptical galaxies are large collections of stars that can contain up to trillions of stars and lack a well-defined structure.
Therefore, the correct option is A) An binary star system is made of two stars.