の After that, some scientists created *incandescent bulbs, but they didn't *last long.
8 So another scientist in the U.S. improved them.
9 They could last very long time.
OIn the 20th century, *fluorescent lights appeared and became popular.
DAlso, in the 21st century, scientists created LED lights and they became popular.
OLight bulbs are necessary for us today.
BA lot of scientists worked hard and created good ones.