Final answer:
Sony can exclusively use the "Walkman" name option (c) because it is a trademark that distinguishes its personal stereos from those of other companies. Trademarks protect brand identifiers and prevent unauthorized use by others.
Step-by-step explanation:
Only Sony can use the "Walkman" name on its line of personal stereos because "Walkman" is a registered Sony trademark. A trademark is a word, name, symbol, or device used in manufacturing or marketing a product that a consumer recognizes as coming from a particular source and distinguishes it from similar products from other sources.
Trademarks are protected by law and they provide exclusive rights to use the name, allowing companies like Sony to prevent others from using it without permission. While patents protect inventions, and copyrights protect original works of authorship such as literature and art, trademarks protect brand identifiers like logos and brand names.
Trade secrets are protected by keeping the information secret and confidential. International laws like those enforced by the World Intellectual Property Organization (WIPO) help to harmonize these protections across different countries.