GRE Reading Comprehension: ETS Official Practice 150-GRE OP150: 阅读 - 6L4ZV4KLT0KC60ZO1

Ragwort was accidentally introduced to New Zealand in the late nineteenth century and, like so many invading foreign species, quickly became a pest. By the 1920s, the weed was rampant. What made matters worse was that its proliferation coincided with sweeping changes in agriculture and a massive shift from sheep farming to dairying. Ragwort contains a battery of toxic and resilient alkaloids: even honey made from its flowers contains the poison in dilute form. Livestock generally avoid grazing where ragwort is growing, but they will do so once it displaces grass and clover in their pasture. Though sheep can eat it for months before showing any signs of illness, if cattle eat it they sicken quickly, and fatality can even result.