What is the difference between prompt and delayed neutrons in a reactor?

What is the difference between prompt and delayed neutrons in a reactor?

• A. Prompt neutrons are emitted within ~10^−14 s of fission; delayed neutrons are emitted by certain fission fragments seconds to minutes later and are essential for control.
• B. Prompt neutrons are slower than delayed neutrons.
• C. Delayed neutrons are emitted immediately at fission, while prompt ones come later.
• D. Prompt neutrons contribute no to reactor control.

Answer: (A)