Class D airspace generally extends from the surface up to what altitude?

Why: Remote Pilot Study Guide (p. 6): "Class D airspace is generally airspace from the surface to 2,500 feet above the airport elevation." A remote pilot must receive ATC authorization before operating in Class D airspace.

• Describes Class B airspace's general ceiling (10,000 feet MSL), not Class D's.
• Describes Class C airspace's general ceiling (4,000 feet above the airport elevation), not Class D's.