A drainage basin is best described as:

A drainage basin is best described as:

• A. The entire area drained by a stream and its tributaries
• B. The region within a river's delta
• C. The area surrounding a lake
• D. The region surrounding a river mouth only

Answer: (A)

The main idea here is what a drainage basin (or watershed) actually covers. It’s the land area where precipitation runs off and drains toward a common outlet—a particular stream or river—through that stream and all of its tributaries. The boundaries are high ground like ridges that form drainage divides, and everything inside those divides eventually flows into that network. So the drainage basin includes the main stream plus every upstream tributary and the land that contributes water to them. That makes the description of the entire area drained by a stream and its tributaries the best fit, because it captures the full network of water collection and transport toward the outlet. The other options focus on specific parts or contexts—such as just the delta region, the area around a lake, or the area near the river mouth only—which do not account for all upstream contributions and the full drainage network feeding the river.

The main idea here is what a drainage basin (or watershed) actually covers. It’s the land area where precipitation runs off and drains toward a common outlet—a particular stream or river—through that stream and all of its tributaries. The boundaries are high ground like ridges that form drainage divides, and everything inside those divides eventually flows into that network. So the drainage basin includes the main stream plus every upstream tributary and the land that contributes water to them.

That makes the description of the entire area drained by a stream and its tributaries the best fit, because it captures the full network of water collection and transport toward the outlet. The other options focus on specific parts or contexts—such as just the delta region, the area around a lake, or the area near the river mouth only—which do not account for all upstream contributions and the full drainage network feeding the river.