Question

the black death in eyam, england
why did half the people in eyam survive the plague outbreak?
o they washed their hands often to keep from getting sick
o they quarantined those who were sick far away from those who were healthy
o they had an unusual genetic mutation that prevented them from becoming infected
o they eliminated the villages rat population, preventing the disease from spreading

Explanation:

The Black Death was a plague caused by the bacterium Yersinia pestis, often spread by fleas on rats. However, in Eyam, a key factor in some surviving was an unusual genetic mutation (the CCR5 - Δ32 mutation) which can prevent certain infections (including some related to how pathogens enter cells). Washing hands (not a common practice with the knowledge then), quarantining (they actually isolated the whole village but the key for survival of half was genetic in modern understanding), and eliminating rats (while a factor in general plague spread control, the specific reason for half - survival in Eyam's context is genetic as per scientific study of the village's descendants).

Answer:

they had an unusual genetic mutation that prevented them from becoming infected