What does the engagement envelope's altitude limit represent, and why does it matter?

What does the engagement envelope's altitude limit represent, and why does it matter?

• A. The altitude range of weather balloons.
• B. The altitude used for navigation charts.
• C. The altitude limit of the terrain map.
• D. The maximum and minimum target altitudes within which the system can reliably detect and intercept; matters due to seeker and motor performance.

Answer: (D)