The question asks which constitutional doctrine is primarily attracted when a pension scheme's cut-off date is challenged as arbitrarily excluding some retirees. Testing each doctrine against what it is actually designed to address helps identify the right fit.
Since the challenge is squarely about whether excluding a class of retirees is a reasonable classification, only Article 14 directly addresses that question; the other doctrines apply to entirely different kinds of constitutional problems.
Therefore, the correct answer is Article 14 and the principle of classification.