阅读理解。

    For years and years people have been saying that railways are dead. “We can do without railways,” people say—as if cars and planes have made railways unnecessary. We all keep hearing that trains are slow, lose money and are dying. But this is far from the truth. In these days of expensive oil, railways have become highly competitive with cars and planes. If you want to carry people or goods from place to place, they are cheaper than planes. And they have much in common with planes. A plane goes in a straight line and so does a railway. What is more, a railway takes you from the heart of a city center. It doesn't stop you as a car does on crowded roads. And no plane or car can ever carry as many goods as one train does.

    Far from being dead, railways are much alive. Modern railway lines give you a comfortable journey. Where else can you eat well, sleep comfortably, feel safe and enjoy the scene while you are traveling at the same time? And we are only the beginning, for we have just entered the age of super-fast trains, which are traveling 150 miles an hour and more. Soon we will be wondering why we spent so much on highways and planes we can't fly in because we don't have enough money to buy the oil.

小远通过查阅资料知道了牙膏的主要成分。它将一定比例的碳酸钙粉末和食盐倒入小烧杯中，然后加入适量甘油（保湿剂）、甜味剂和香精等，搅拌均匀后制得牙膏。
（1）牙膏是____ （填纯净物、混合物）。
（2）小远测定自制牙膏及其他清洁用品的pH，记录如下：

自制牙膏显____ （填“酸性”、“碱性”、“中性”），洁厕灵可使紫色石蕊试液变成____ 色。
（3）下表列出了三种牙膏摩擦剂所属的物质类别。

（4）牙膏中的摩擦剂之一碳酸钙可以用石灰石来制备。某学生设计了一种制备碳酸钙的实验方案，其流程图为：
石灰石生石灰石灰水  碳酸钙
请写出上述方案中有关反应的化学方程式：
①____ ②____③____ 。

如图所示是弹簧振子的振动图象，请回答下列问题．