Both the Mothers and Children Shown Below Have Breathed in Polluted

Both the mothers and children shown below have breathed in polluted air over a period of time, yet only the child shows symptoms of environmentally linked respiratory diseases and is receiving treatment. This is so because:

A) A child has a higher metabolic rate and needs more oxygen, so he takes in more air.
B) Adults living in these areas have developed a tolerance to the air pollutants that are present there.
C) There are no known treatments available to treat adults suffering environmentally linked respiratory diseases.
D) Young children show symptoms earlier than adults do.