please be my tutor, this made me understand it ten times better

I'm still really struggling to understand why A is incorrect because in the first sentence, we're using the word "average" from the pov of government statistics but in the conclusion, we're using the word "average" in terms of the pov relative to other families....I thought A was a sure fire winner....

lsac you will begin to cough in 7 days

this is insane omg, why is it not E