When corn came to Europe from Mexico, now they had a much hardier crop that could be grown easily in more northerly climates and the centers of power began to shift accordingly.
当玉米从墨西哥传到欧洲的时候，他们有了一种更耐寒的作物，更容易在更偏北的气候条件下种植，权力的中心也随之转移。
The queens taken from these hives are then placed in new hives, exposing them to even more "disease pressure." The theory is that each generation of survivors will be hardier than the last.
首先，研究者发现了一种对螨虫具有抵抗力的蜂群，将这种蜂群的蜂王置于新的蜂房中，并对它们进行更为严酷的疾病考验，经过一代又一代的筛选，存活下来的新品种的抵抗能力将越来越强。
The queens taken from these hives are then placed in new hives, exposing them to even more "disease pressure." The theory is that each generation of survivors will be hardier than the last.
首先，研究者发现了一种对螨虫具有抵抗力的蜂群，将这种蜂群的蜂王置于新的蜂房中，并对它们进行更为严酷的疾病考验，经过一代又一代的筛选，存活下来的新品种的抵抗能力将越来越强。
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