Explanation:

Macintosh, commonly shortened to Mac, is a series of personal computers designed, developed, and marketed by Apple Inc. since 1984. The Mac line includes various models such as desktop computers (e.g., iMac, Mac mini, Mac Studio) and laptop computers (e.g., MacBook Air, MacBook Pro). These computers are known for running Apple's macOS operating system. Option (b) 'Dell', (c) 'Acer', and (d) 'HP' (Hewlett-Packard) are other prominent manufacturers of personal computers, but they primarily produce Windows-based PCs or Chromebooks, not Mac computers. Therefore, Apple is the sole manufacturer of Mac personal computers.