Answer:
See the answer below
Step-by-step explanation:
Since no fresh air is coming into the elevator while the people are still trapped in it, the breathing of the people will alter the composition of the air inside the lift.
Breathing involves taking-in of oxygen and the release of carbon dioxide. Hence, less and less oxygen will become available within the lift while the concentration of the carbon dioxide keeps increasing as time goes on.
If the people remain trapped for a long time, the oxygen composition of the air inside the elevator will become exhausted, the carbon dioxide concentration will increase, and the people will suffocate due to lack of oxygen.