Answer:
C. a region where many asteroids are located
Step-by-step explanation:
One of the most effective ways to learn new words or to infer their possible meaning is from the context of the adjacent sentences.
Here the underlined words are "asteroid belt". And just after that there is an expenation to these words.
It says it's a specific, precisely defined region of space (between Mars and Jupitet) where great number of asteroids can be found.
So, the best fitting answer for this would be option C.