Numbers 31 to 33 refer to the following passage.
Approximately 74,000 years ago on the island of Sumatra, Indonesia, a volcanic eruption so violent occurred that it proved to be (1) ... for the human race. Scientists estimate that the eruption may have ejected up to 6,000 km3 of magma and pulverized rock and sufficient sulfur gases to form 5,000 megatons of stratospheric sulfuric acid aerosols. The suspension of so much material in the earth’s atmosphere resulted in a volcanic winter that lasted all year long,'c'very year for several years. The (2) ... in global temperatures had catastrophie effects on vegetation and the food chain dependent upon it for survival - including humans.
Scientists have examined the genetic codes ofseenringly disparate and distant races of people and found there’s actually very little genetic variability in the entire human race. The evidence indicates that something happened to the human gene pool approximately 74,000 years ago where only very few humans remained alive on the planet (say 5,000 to 10,000), and the current population has grown from these selectively few genotypes. (3) ... is a testament to our tenacious ability to survive.
The option that best completes (1) is....