People have used glass for thousands of years. While most glass has been manufactured, some kinds of glass occur naturally. Obsidian is a type of glass formed when lava from a volcano cools and hardens. Prehistoric people used obsidian to make arrowheads, blades, and tools. Their edges are sharper than steel blades! Glass also can form when lightning strikes a sandy place, such as a desert or a beach. The heat from the lightning melts the sand, and a kind of glass called fulgurite is formed. 2Glass has many special properties. Even though it is hard, it is not really a solid. The molecules in a solid are arranged in a pattern, but the molecules in glass harden without forming a pattern. Although it is brittle and breaks easily, glass is very strong in other ways. It can withstand heat as well as cold, so it can be used to cook food. It is also useful for laboratory equipment such as test tubes and beakers. Adding a variety of colors to clear glass can produce beautiful works of art. Glass has been used to make many things, including beads, eyeglasses, bottles, lamps, microscopes, windows, and lightbulbs. 3Glass is made by mixing silica, which is a common kind of sand, with other minerals. Until 50 BCE, glass objects took lots of time and effort to create, so only small numbers of them were made. Because glass was so difficult to make, it was an expensive luxury item. Then, in 50 BCE, Romans living in Phoenicia (now Lebanon) discovered the technique of glassblowing. A glassmaker places a blob of molten glass on the end of a pipe and blows through the pipe to shape the glass. Then, it is put into a mold or shaped with tools. At this stage, the glass is much like clay, and the glassmaker often rolls it on a table made of iron or marble to shape it. Designs can also be cut into the glass after it hardens. When the glass cools, it is hard and shiny. 4As a result of this new technique, glass objects of many sizes and shapes could be made quickly. Ordinary people, not just the very rich, could now purchase glass. Early glassmakers figured out how to make colored glass by adding different ingredients. They learned how to make beautiful cameos. To make a cameo, the glassmaker encloses a glass object in layers of colored glass, and then cuts designs into the layers. Cameo glass was made all over the Roman Empire, as well as in China. The Roman Empire encouraged the production of beautiful and functional glass objects. 5In 1291, an interesting episode in the history of glassblowing happened. At that time, all the glassmakers of Venice, Italy, were sent to the island of Murano. Back then, Venice was one of the world's main centers of trade, and ships constantly sailed into and out of the bustling city. But most of its buildings were made of wood, and the Venetians didn't want the furnaces used by glassblowers to put the city at risk of a fire. All the glassmakers were ordered to move their shops to the nearby island. By 1296, the government realized how important the skilled glassmakers were to Venice, and the glassmakers were forbidden to leave. To appease the restricted workers, glassmakers were given higher social status and were permitted to marry into Venice's richest families. Glassmakers were not allowed to teach their skills to foreigners, though, because the glassmakers were the only people in Europe who knew how to make certain kinds of glass. For hundreds of years, Murano was the chief glassmaking area in Europe. Despite the restrictions, however, many glassmakers escaped from Venice and took their skills across Europe. By the sixteenth century, France, Germany, England, and the Netherlands began to produce their own versions of Venetian glass. 6Today, most blown glass used in homes or laboratories is made in factories. However, there are still many glassblowers who create beautiful glass pieces by hand. These artists often give classes and demonstrations to teach their skills to others. If you ever have a chance to watch a glassblower in action, you will see an art that has existed for thousands of years. Which of the following statements BEST describes the central idea of the text?

A. The evolution of glassmaking has survived many years, yielding various forms, and cutting across broad groups of people.
B. Glassblowing allowed poorer people to produce glass like the richer people.
C. There are various types of glass that have been used across the centuries.
D. The properties in glass allow it to be used to produce various objects.