Which of the followings can best replace the word "eye strain" in paragraph 4?

4. What does the word “its” in the last sentence refer to?

3. How many hours did the 1880 bulb last?

2. Where was Edison’s laboratory?

Read the following passage, and choose the best answer that follow.

Thomas Alva Edison was born in Ohio in 1847. As a child, he received less than a year of formal schooling, but was educated at home. His parents allowed him to set up a laboratory in their basement and his mother gave him books about chemistry and electronics. Edison credits his mother as being ‘the making’ of him.

In 1878, Thomas Edison began serious research into developing a practical incandescent lamp and on October 14, 1878, Edison filed his first patent application for "Improvement In Electric Lights". In 1879 he created a successful incandescent light bulb. This was his hardest project – from 1877 to 1880, Edison and his assistants tried around 3000 experiments to perfect their light bulb design. By the end of 1880, Edison had produced a bulb that lasted 1500 hours. This discovery marked the beginning of commercially manufactured light bulbs and in 1880, Thomas Edison’s company, Edison Electric Light Company began marketing its new product.

5. What did her parents do?

4. How long did she travel in the space shuttle Challenger?

3. When did she become America’s first spacewoman?

2. What does she look like?

1. Who is America’s first spacewoman?