W: I need to make sure you understand how to get housing for next year. When you entered as first year students this year, the school assigned you to a dorm and a roommate. But next year as returning students, you’ll choose both your roommate and your dorm. But whether or not you actually get to live in your first choice depends on what number you or your roommate draws in the lottery system. The system gives priority to the students who have been here the longest. Fourth year students get the first block of numbers, third years students get the second block and second years, like you’ll be, get the third. The lower the number you draw, the sooner you choose. No. 1 gets the first choice, No. 2 gets the second choice, and so on. You can use either your own or your intended roommate’s number to make your room choice. If your roommate for next year has been in the school longer than you have, they’ll be in a better block of numbers and so will have a better n
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 ou
A. healthy people should live separately from unhealthy members of the family
B. a germ-free home is not only possible, but significant
C. unless you live with the vulnerable, it is pointless to sterilize the air
物体同时受到同一平面内三个共点力的作用，下列几组力的合力可能为零的是（）
我来回答:
