The amount of water is the same as the _____.

• A. Beginning of Time
• B. Clean Water
• C. Ocean Depth
• D. Rainwater

Answer: (A)

The key idea is that water on Earth is part of a mostly closed system and is continually recycled through the water cycle. Water evaporates from oceans and other bodies, rises and condenses into clouds, then falls as precipitation, feeding rivers, lakes, and the land again. This cycle moves water around but doesn’t significantly change the total amount available. Because of that recycling, the planet’s total quantity of water has remained essentially constant since its formation, so it’s the same as at the Beginning of Time. The other options point to a form or measurement of water (quality, depth, or a portion of the supply) rather than the total global amount.