【正确答案】 D

【答案解析】原文：The amount of plastic waste flowing into the ocean could triple in 20 years unless businesses and governments act to reduce plastic production.That warning comes from a new study that appeared recently in the publication Science.The study, called “Breaking the Plastic Wave”, identified measures that could reduce plastic pollution that gets into the ocean by 80 percent.If no action is taken，however，the amount of plastic going into the sea every year will rise from 11 million metric tons to 29 million metric tons by 2040，the study said.根据新闻定位句可知,研究表明我们的祖先的睡眠时间并不比我们多,他们平均每晚睡6.5小时。也就是说，一晚上平均睡眠6.5小时是正常的时长。故选D。