Example: Why       did      people      use   to     read by the fire at night?

A. did/ use to                      B. do / used to                 C. did / used to

1. People ______________________ have electric lights.

1. A. didn’t used to                             B. didn’t use to                 C. did use to

2. 2. It was difficult to see at night. The electric light was a good _______ to a big ________.

1. A. solution / problem                   B. problem / solution         C. used / problem

3. 3. The electric light is a ___________________________.

1. A. useful problem                 B. useful solution              C. useful invention

4. 4. Do you think you need a good ____________________ to _____________ things?

1. A. solution / invent               B. imagination / invent    C. problem / invent

5. 5. Yes, I do. __________ must have many good __________.

1. A. You / ideas                      B. He / problems              C. You / solutions