From the book, I learnt that there have been many changes to this place.

通过这本书，我了解到在这个地方有许多变化。

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This week, epidemiologists will try to find out how many people each infected person spreads the disease to, and how this figure changes with time and place.

本周，流行病学家们要设法查清：每一个感染者会传染多少人；这个数字如何随时间和地点而变化。

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