**Core Concept:** Grammar - Tense Usage **Analysis:** Present Simple (C) is standard for stating established scientific facts (e.g., 'Studies show...'). Past Simple (A) describes specific past events. Present Perfect (B) links past to present, and Future Continuous (D) is irrelevant for general truths. **Key Point:** Universal truths use Present Simple. **Common Mistake:** Misusing Past Simple for timeless facts due to narrative habits.