This question can be approached by first naming what the excluded employees are actually complaining about, and then matching that complaint to the constitutional doctrine designed to address it.
Since the complaint is specifically about unequal treatment through classification, the doctrine that squarely applies is Article 14's reasonable classification test.
The correct answer is Article 14 and the principle of classification.
A useful check here is to ask, for each option, what question is this doctrine actually designed to answer, and then see which of those questions matches what the excluded employees are asking the court to decide.
Matching the real question being asked in the facts, whether unequal treatment through a cut-off date is justified, to the doctrine that answers exactly that question points to Article 14.
So the correct answer is Article 14 and the principle of classification.