She was a milkmaid. She had to get up very early every morning and go to the barn to milk the cow.

VOA: special.2010.11.20

It's a big change in some of these very poor villages to get a cow.

奶牛对这些赤贫的村庄来说可是生财之道

耶鲁公开课 - 金融市场课程节选

So, it's awkward to have to wait for a cow to get infected before you can vaccinate a population.

在给人们预防接种之前,你只有干等着,直到有一头奶牛感染了病毒才行

耶鲁公开课 - 生物医学工程探索课程节选