果园里有苹果树412棵，平均每棵收苹果150千克，卖出50000千克，还剩（   ）

阅读下文，回答相关问题。
        去除饮水中可能致命的细菌或许会成为纳米管最早的实际用途之一。
        科研人员已经研制出能让细菌聚结成块的纳米管，随后就可以将菌块从水中滤出，并消灭它们。他们进行的实验很容易用于实践。
        南加州克来姆森大学负责此项研究的孙亚平说，这种纳米管最初或可以用作水净化处理厂的过滤器。他的研究成果发表在最新一期的《化学通讯》杂志上。
        新研制的纳米管能捕捉大肠杆菌O157：H7，即臭名昭著的“汉堡细菌”，被它污染的肉可能置食客于死地。他给纳米管表面覆上一层半乳糖分子，而半乳糖分子能与大肠杆菌表面的受体蛋白粘合。每根纳米管都覆有数以百计的半乳糖分子，因此能一举拿下大量细菌。
        该研究小组还研制了能捕捉污染事物的另一种常见细菌――空肠弯曲杆菌――的纳米管。这种细菌多见于肌肉之中。这一次纳米管的表面富有甘露糖分子，它能与空肠弯曲杆菌表面的受体蛋白粘合。孙说：“我们正在研制富有能捕捉不同细菌的多种配位体‘糖’的纳米管。这是可行的。”
        研究者认为，从理论上说，这种纳米管可以用于将细菌从患者的血液中滤出，不过它们必须首先经过试验，排除任何毒副作用的可能。英国史密斯叔侄公司的彼得·阿诺得说：“将来，类似于这类碳纳米管的交互性生物材料有望选择性地捕捉和消灭致病细菌。”该公司是一家医疗技术公司，正在研制能加快组织修复的生物材料。
        研制临床诊断用的纳米材料的英国奥克斯尼卡公司的凯文·马修斯说，孙的工作是传统无机化学与生物化学相结合的极好例子，二者结合“提供的可能性超越了其中任何一种单独所能提供的可能性。”

                                                                                                                                                            摘自2005年3月12日《参考消息》
       注：“半乳糖”和“甘露糖”是配位体糖的两个具体种类。

促使孙中山放弃改良走上反清道路的直接原因是    (　　)。

    Fresh off his MasterChef Junior run, Evan Robinson, who is only 12 years old, is using his kitchen skills to raise money for Puerto Rico. The TV show contestant wanted to offer help after hurricanes(飓风) hit the country last September.

    “I've been seeing, all over the news, people struggling,” Evan said. “They can't get fresh water, electricity; they can't get really anything. I know I'm just a kid, but I think if a lot of people do something, a lot of things will get better.”

    He raises money by baking and taking online orders for homemade empanadas(馅 饼). He started cooking on a recent Friday night. By the next Sunday evening, he had filled orders for 420 empanadas — — roasted chicken, cheeseburger and vegetarian — — getting $18 for six empanadas and $30 for a dozen.

    His mom, Veronica Robinson, helped him send the empanadas around the city. “We've never done anything like this before,” she said. “But it's a great idea, so I want to help him make it work.”

    For Evan's out-of-town friends and supporters, he has set up a crowdfunding(众筹) page. Through it, he's hoping to raise $1, 500 in “virtual (虚 拟 的) empanadas”. This is because he heard on the news that it could take Puerto Rico years, maybe  even 10 years, to recover(复 原) from the hurricanes. And he said, “Fruit pies are up next. And my baking will continue as well.”

    It's a difficult job, especially for a kid with homework and Boy Scouts and friendships to tend to. But he doesn't seem worried.

    “It's what we're supposed to do.” he said. “I'm a human. They're humans. Why shouldn't I help them?”

    Indeed.

下列划线字注音正确的一项是(    )