UPSC Prelims 2014— Question 80

Correct answer: Option A. In a simple aquatic food chain, phytoplankton such as diatoms are primary producers, small crustaceans such as zooplankton consume them, and herrings can feed on those organisms. Therefore the sequence producer → primary consumer → higher consumer is diatoms → crustaceans → herrings. Option A: Correct. This option is consistent with the governing fact or the valid combination identified in the question. The option reads: “Diatoms-Crustaceans-Herrings” Option B: Incorrect. This option does not match the verified answer because its proposition, location, institution, sequence, or combination conflicts with the relevant fact tested in the question. The option reads: “Crustaceans-Diatoms-Herrings” Option C: Incorrect. This option does not match the verified answer because its proposition, location, institution, sequence, or combination conflicts with the relevant fact tested in the question. The option reads: “Diatoms-Herrings-Crustaceans” Option D: Incorrect. This option does not match the verified answer because its proposition, location, institution, sequence, or combination conflicts with the relevant fact tested in the question. The option reads: “Crustaceans-Herrings-Diatoms” The key Prelims lesson is to test each proposition independently before selecting the combination. Where the question uses words such as 'only', 'all', 'none', 'always' or a precise institutional/geographical association, a single inaccurate component is sufficient to eliminate the option. The answer recorded here follows the official answer key for the question-paper series represented by the uploaded source and has been cross-checked against an independent published key. The explanation is intended for conceptual revision rather than as a reproduction of any third-party solution.