Concept:Respiration in a closed space uses up oxygen and cannot replace it, leading to suffocation.
Explanation:The student kept breathing inside the sealed cupboard.
During respiration, the body takes in oxygen (
O2) and releases carbon dioxide (
CO2).
Because the cupboard is airtight, no fresh air can enter.
So the available oxygen is steadily consumed and becomes too little to support life.
Low oxygen causes hypoxia, and vital organs fail, resulting in death.
This does not mean all air disappears; the larger part of the oxygen is used up.
Answer:B. The greater part of oxygen in the cupboard was used up.