The key answer of exercise 7
The key to exercise solutions in chapter 4c - Grammar in use for the textbook On Screen B1+ - Student's Book with authors Virginia Evans and Jenny Dooley from Express Publishing
Question
Collect information about how glass is made. Present the process to the class. Use the passive.
Answer
Glass is made by melting sand, or silicon dioxide. Other ingredients are added in small amounts, such as sodium carbonate. The furnace is heated to around 1700C. The mixture is poured onto a bed of liquid metal to form sheets. If the glass is being used to make a container or bottle, it is pressed or blown.