[单项选择]

I saw a television advertisement recently for a new product called an air sanitizer. A woman stood in her kitchen, spraying the empty space in front of her as though using Mace against an imaginary assailant. She appeared very determined. Where others are satisfied with antibacterial-laced sponges, dish soaps, hand sanitizers and telephone wipes, here was a woman who sought to sterilize the air itself.|
As a casual student of microbiology, I find it hard to escape the absurdity here. This woman is, like any human being, home to hundreds of trillions of bacteria. Bacteria make up a solid third, by weight, of the contents of her intestines. If you were to sneak into her bathroom while she was showering-and based on my general impression of this woman from the advertisement, I don’t recommend this-and secret away a teaspoon of the water at her feet, you would find some 820 billion bacteria. Bacteria are unavoidably, inevitably-and, usually, utterly benignly-a part of o
A. if he washes his hands every time he touches a surface
B. if he only washes his hands with soap and water
C. if he could not win over the bacteria in his home
D. if he does not fight against the bacteria at home