Open work spaces definitely have their benefits，but they come with the drawback of offering employees little to no control over visual distractions(干扰)．With so many people around and so much going on，some of us can easily get disturbed by this information overload and lose focus in what's really important．That's where the Focus Cap comes into play．

    “As we are still cavemen or mammals kept in an unnatural environment，I believe that only by reclaiming(收回)the normal，stress-free human state through simple tools and techniques can we finally release our actual creative potential and create our meaningful work for a brighter future，”says German designer Hannes Greblin，inventor of the Focus Cap．

    After looking at other products designed at minimizing visual distractions，Greblin decided that most of them were either too expensive or too uncomfortable to become mainstream，so he decided to go with something much simpler —a simple cap with a retractable visor(可伸缩的帽沿)．

    Greblin's Focus Cap is really straightforward．You just wear it like a regular cap'with the sides of the visor retracted，and just collapse the sides whenever you need to focus on what's ahead of you．Whether you're trying to focus on a task in an open work office．Trying to study at university，or practicing yoga in a park and trying to ignore stares from strangers，the Focus Cap can help．

    To be honest，this whole project sounds like a joke，but the Focus Cap does have its own website where people interested in this unusual accessory can actually sign up for updates on when it will go on sale．Greblin claims it will cost 30 euros($37)plus shipping．

某些媒体报道“转基因植物油对人类的健康不利”，也有专家说“转基因植物油是安全的”，到底是否安全呢？某班初二学生针对这一问题进行了如下探究实验．

（一）实验器材：普通植物油，转基因植物油，稻谷若干，小白鼠若干，两个规格一样且空间足够大的铁笼等．

（二）该同学提出的问题：转基因植物油对人类的健康是否有影响．

（三）实验过程：

（1）将两个铁笼分别贴上甲组和乙组标签，选取两只身体健康状况良好、大小一致、性别相同的小白鼠，分别置于甲、乙铁笼中．

（2）称取一定重量的同种稻谷平均分成两份，分别拌适量且等量的普通植物油（A料）和转基因植物油（B料）待用．

（3）甲组饲喂适量A料，乙组饲喂____ B料．

（4）饲喂一段时间后，观察并记录甲、乙两组小白鼠的生长状况．

（5）预测实验结果和结论：

①若两组小白鼠的生长状况有明显差异，则说明转基因植物油对人类健康____ （填有或无）影响．

②若两组小白鼠的生长状况无明显差异，则说明转基因植物油对人类健康____ （填有或无）影响．

（四）请根据上述实验设计回答下列问题：

（1）请你为该同学做出假设，你的假设是：____ 

（2）该同学设置甲组的目的是对照，该实验的实验变量是____ 

（3）该实验选取小白鼠的数目过少，会增大实验的____ ，导致实验结论可信度不高．

用反证法证明：“三角形三内角中至少有一个角不大于60°”时，第一步应是（　　）