The water cycle is maintained mainly by

Analyze the question: It asks what mainly maintains the water cycle, meaning the processes that keep water continuously moving between the earth and the atmosphere.

Explain the concept: The water cycle (hydrological cycle) is a continuous loop:

1. Evaporation: The sun heats water in oceans, rivers, lakes and soil, and it turns into water vapour. Plants also lose water vapour by transpiration.
2. Condensation: The water vapour rises, cools and forms clouds.
3. Precipitation: The water falls as rain, hail or snow.
4. Runoff and infiltration: The water returns to rivers, seas and underground, ready to evaporate again.

Step-by-step solution:

• Option A (evaporation only): Evaporation puts water into the air, but without condensation the water would never return as rain. The cycle would be incomplete.
• Option C (condensation only): Condensation needs water vapour to be there already, and evaporation supplies it. This option is also incomplete.
• Option D (transpiration and respiration in plants): Transpiration contributes some vapour, but respiration is not a major part of the water cycle. Plants are only a minor contributor compared with oceans and other water bodies.
• Option B (evaporation and condensation): These two processes form the main "up and down" link of the cycle. Evaporation sends water up as vapour and condensation brings it back toward the earth as clouds and rain. Together they keep the cycle going.

Answer: B. Evaporation and condensation of water in the environment

Exam tip: When a question asks what "maintains" a cycle, pick the option that includes both the step that sends water up and the step that brings it back. Single-process options like A and C are usually traps. Remember: Evaporate up, Condense into clouds, then rain falls.