3. Choose the correct answers. The light bulb
What would we do without electric lights? In the 1800s, light bulbs ' _by
different people, but none of them were good enough to sell until the right
material to go inside the bulb?
— Thomas Edison. Since then, electric lights
- around the world by billions of people.
The original designº— much, although more energy-efficient light bulbs
now in many parts of the world. However, in some countries, people can't
afford to use electricity. This fact encouraged U.S. teenager Ann Makosinski
to invent a new kind of light. This light ® __by electricity. It uses body heat
instead. But '_replaced by this new invention in the future? Probably not, but
light — and so this invention could definitely become popular in many parts
of the world.

1. a) are developed b) developed c) were developed d) is develop
2. a) were discovered by b) was discovered c) was discovered by d) were discovered
3. a) have used b) have been used c) have be used d) have use
4. a) isn't changed b) won't change c) hasn't been changed d) hasn't be changed
5. a) will be bought b) is bought c)are bought d) were bought
6. a) isn't powered b) wasn't powered c) hasn't powered
d) not powered
7. a) will be the light bulb b) will the light bulb be c) will the light bulb d) the light bulb
8. a) will be always needed b) always will be needed с) will be needed always d) will always be needed​