UPSC Prelims 2018— Question 99

**Concept and analysis:** Plant pathogens and disease agents can be dispersed by several natural and physical vectors. Wind can carry spores and infected plant material; dust can transport pathogens; birds can carry infectious agents or contaminated material; and rain splash can disseminate pathogens over short distances. Therefore all four listed mechanisms can contribute to the spread of plant diseases. The question is testing precise UPSC-level identification rather than a broad association. The key is to distinguish the exact institutional, constitutional, historical, geographical, economic or scientific feature being asked. **Option-wise evaluation** **Option A:** Incorrect. It selects 1 and 3 only, but that combination does not match the verified statement-level assessment; it either includes a false statement or omits a true one. **Option B:** Incorrect. It selects 3 and 4 only, but that combination does not match the verified statement-level assessment; it either includes a false statement or omits a true one. **Option C:** Incorrect. It selects 1, 2 and 4 only, but that combination does not match the verified statement-level assessment; it either includes a false statement or omits a true one. **Option D:** Correct. It selects statements 1, 2, 3, 4; these are the statements supported by the relevant constitutional, economic, historical, scientific or geographical facts. **UPSC takeaway:** The safest way to solve this type of question is to anchor the answer in the defining feature of the concept and then test every option against that feature. Closely related institutions or terms are often used as distractors. In statement-based questions, do not judge the option as a whole before checking each statement independently. In factual questions, compare the wording of each option with the exact definition, location, institutional role, chronology or scientific property. The correct answer follows from that verification rather than from familiarity with a keyword.