语法填空

    Green is not always referring to the color. In some cases, it is the term used for environmental____(friend). If you've been expecting to replace your furniture, consider ____(go) green because green furniture offers many benefits. Here are a few tips to get you started on your hunt for the perfect eco-friendly furniture.

    First, green furniture isn't harmful____your health. Also its making process doesn't cause damage to the environment in any way. Besides, by using eco-friendly ____(product), you prevent global warming to some degree in your own way.

    The materials____are used in furniture are what make them green. Materials can be good for the environment ____ because they are renewable resources or they are all ____(nature). A lack of chemicals in furniture also____(mean) it is a better choice for the environment. It may be hard to imagine that a sofa or a table could actually be____green product, but they really can be depending on what they ____(make)of.

    Therefore, when you want to hunt for the perfect green furniture, you should choose the green materials.

我国唐代诗人王维诗云：“明月松间照，清泉石上流”，这里明月和清泉，都是自然景物，没有变，形容词“明”对“清”，名词“月”对“泉”，词性不变，其余各词均如此．变化中的不变性质，在文学和数学中都广泛存在．比如我们利用几何画板软件作出抛物线C：x²=y的图象（如图），过交点F作直线l交C于A、B两点，过A、B分别作C的切线，两切线交于点P，过点P作x轴的垂线交C于点N，拖动点B在C上运动，会发现 $\frac{\left|NP\right|}{\left|NF\right|}$ 是一个定值，该定值是____．