In the Section "Investigating Life: the Hidden Cost of Hygiene

In the section "Investigating Life: The Hidden Cost of Hygiene," what is the hygiene hypothesis?

A) People who have more infections will have an overactive immune system.
B) People who have better hygiene and are cleaner will have more infections.
C) People who have better hygiene and are cleaner will have a weaker immune system.
D) People who have fewer infections will have an overactive immune system.
E) People who have better hygiene and are cleaner will have fewer infections.