You have to test it by giving the vaccine to a large population of people, and then watching and seeing if you've reduced the incidence of the disease.
这样的测试的做法只能是,给大量人群分发疫苗,接着观察和了解,这种疾病的发病率是否有所降低
You're not intervening with people, you're observing usually large numbers of people in a population.
不干涉他人生活,只是观察一个人群中的许多个体
Northern Italy has a large percentage of the population who are middle class.
意大利北部有很大比例的中产阶级
That explains, in large part, why there was such a decline in population, why the Dark Ages were so dark, lots of poverty, lots of starvation, but also, as I suggested when I spoke of this earlier, also the freedom if you could make it, to learn and also to grow stronger.
这解释了,在绝大部分地区,为什么存在着这一类的人口消减,为什么黑暗时代如此黑暗,如此贫困,如此多的饥荒,但是同时,就如在我之前所提到的,同样可以,如果做得到的话,去学习以及使自身强大
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