And without a vaccine, Dr.Fauci says the best methods of prevention are these: encourage people to limit the numbers of sexual partners encourage men to use condoms train more doctors to perform adult male circumcision empower women to choose their sex partners and protect themselves from getting the virus that causes AIDS All of these goals still remain major challenges.

VOA: standard.2010.07.17

So the problem I want to do-- there are many things you could do but I just picked one, and this is the one with round numbers, so I can do it without a calculator.

我想讲的这道题,类似的题目很多,但我就选了其中一个,这道题涉及的数字都是整数,所以我不需要计算器

耶鲁公开课 - 基础物理课程节选