Which statement describes viruses?

• A. Commonly spread by aphids, leafhoppers, and thrips.
• B. Microscopic roundworms.
• C. Includes powdery mildew and rust.
• D. A type of bacterium.

Answer: (A)

Viruses in plants are tiny infectious agents that rely on plant cells to reproduce, and they are typically spread by insects that suck sap from plants. Aphids, leafhoppers, and thrips are well-known vectors that can transmit viral particles as they move from one plant to another, making this type of transmission a hallmark of plant viruses. The other statements describe entirely different organisms or disease-causing agents: microscopic roundworms are nematodes, powdery mildew and rust are caused by fungi, and bacteria are a separate category of microorganisms. Therefore, the description of being commonly spread by those sap-sucking insects best captures how viruses move in plant systems.