Final answer:
The appropriate word to complete the sentence is 'competitive,' indicating a market with active rivalry and efforts to attract customers among gunshot detection system providers.
Step-by-step explanation:
A number of gunshot detection systems currently compete in the competitive civilian market. The correct word to fill in the blank is 'competitive', reflecting the intense rivalry among companies to capture market share with their gunshot detection technology. In a competitive market, different businesses strive to offer better features, pricing, and technology to attract customers, often resulting in fast-paced innovation and aggressive marketing strategies.