Explanation:

TeachText was a simple text editor and viewer application that was specifically included with the classic Mac OS operating system, serving as its default text editor in early versions. Therefore, option (d) 'Macintosh' is the correct answer. Option (a) 'Windows' is an operating system by Microsoft, which uses Notepad or WordPad as its default text editors. Option (b) 'Google Chrome' is a web browser, not an operating system, and does not have a built-in text editor called TeachText. Option (c) 'Mozilla Firefox' is also a web browser, not an operating system, and similarly does not feature TeachText. The association of TeachText is exclusively with the Macintosh platform.