单选题 Humans derive about 20% of their protein from animal-based products now, but this may need to drop to just 5% to feed the extra two billion people expected to be alive by 2050, according to research by some of the world"s leading water scientists.
【正确答案】 A
【答案解析】[解析] 一些世界顶尖水资源科学家的研究表明，现在人类从动物类食品中汲取了大约20%，的蛋白质，但是到2050年这一数据需要下降到5%，因为到那时我们还需要养活另外大概20亿人口。这句话语意完整，没有什么明显的语法错误。