Which of the following is not a software process model?

Explanation

Prototyping, the iterative (iterative enhancement) model and time-boxing are all genuine software process models — time-boxing in particular is the iterative model with fixed-duration iterations whose scope, not whose schedule, is allowed to vary. Glass-boxing is not a process model at all: "glass box" (or clear box) is simply another name for white-box testing, a test-case design technique based on the internal structure of the code. Confusing a testing technique with a life-cycle model is what this question tests, so the answer is glass-boxing.