A – Wrong
Oxygen demand is more than oxygen demand. Since there is a lack of oxygen, anaerobic respiration must be taking place. However, there is still some aerobic respiration taking place as oxygen is present. Therefore, this is wrong as both aerobic and anaerobic respiration is taking place and not only anaerobic.
B – Wrong
This is clearly wrong as the line for oxygen demand is higher than oxygen supply.
C – Wrong
Again, both anaerobic and aerobic respiration is taking place. This is wrong.
D – Correct
Both aerobic and anaerobic respiration always take place.