Read the following passage and choose the item (a, b, c, or d) that best answers each of the questions about it.
The first computers were very large machines. Now computers come in all shapes and sizes. There were still big computers for companies or universities. There are other special computers for factories. These large computers tell the factory machines what to do. But there are also small personal computers to use at home or in an office. There are even computers in telephones, television sets, and cars. These computers have to be very small. They are so small you cannot even see all their parts.
What does the word ‘they’ in line 7 refer to?
telephones television sets cars computers