Via the half-life equation:

Where the time elapse is 11,460 year and the half-life is 5,730 years.

Therefore after 11,460 years the amount of carbon-14 is one fourth (1/4) of the original amount.
The answer is D. As the ambulance gets closer, the sound waves are compressed relative to the person; so the frequency increases.
fault-block mountains. hope this helps