Which statement is true about the descent guidance 'Descend and maintain' versus 'Descend FL240 at pilot's discretion'?

• A. Descend and maintain: You may descend any time and at any rate; At pilot's discretion: Begin descent on readback.
• B. Descend and maintain: Begin descent upon readback, and at a standard rate of descent; At pilot's discretion: Can descend any time and at any rate.
• C. Descend and maintain: Descent must begin immediately; At pilot's discretion: Descent rate is fixed.
• D. Descend and maintain: Descent must be completed before reaching FL240; At pilot's discretion: Descent is not allowed.

Answer: (B)

The key idea is that clearance wording sets who controls the timing and how you execute the descent. When ATC says descend and maintain a certain altitude, you’re cleared to descend to that altitude and then hold it. The usual practice is to begin the descent after you read back the clearance, and follow a standard rate of descent unless a different rate is specified. In contrast, if the clearance uses “at pilot’s discretion,” the pilot gains control over both when to start the descent and how fast to descend, within safe and ATC constraints.

So the statement that matches this is: you begin descent on readback to reach the assigned altitude and use a standard descent rate, while the pilot’s discretion version means you can descend at any time and at any rate.