Because Astronomers use light-year instead of kilometers to measure distances in the universe because distances in space are so huge that km would be too large to manage.
Answer:
Relevant.
Explanation:
Relevant is a descriptive word for a topic useful to society's progress.
In improving the development and continuous growth of a society, it is very important and essential to identify or establish topics that bear or have a significant impact on the society. This type of topics that have a positive impact on the growth and development of the various aspects of a society are said to be relevant because they play a vital (significant) role in the progress of a society. Synonyms for relevant are pertinent, germane, significant, apposite etc.
Some examples of relevant topics (topics useful) to the progress of a society;
1. Research on how to create more jobs.
2. Improving citizen's security through CCTV.
3. How to combat banditry and terrorism.
4. Effects of drug abuse among teenagers.
