ĐỀ THI IELTS READING VÀ ĐÁP ÁN - The History of Glass
The History of Glass
From our earliest origins, man has been making use of glass. Historians have discovered that a type of natural glass - obsidian - formed in places such as the mouth of a volcano as a result of the intense heat of an eruption melting sand - was first used as tips for spears.