Which one of the following statements is not correct with regard to the UNIX operating system?

Statement (d) is incorrect: UNIX was DESIGNED as a time-sharing operating system that allows multiple users to share computing resources simultaneously — this is one of its defining features. Statement (a) is correct: UNIX is largely written in the C programming language. Statement (b) is correct: being written in C made UNIX portable across many hardware platforms. Statement (c) is correct: UNIX is a multi-user, multi-tasking operating system. Hence option (d) is not correct.