Have you found a .................. to that math problem

1. Have you found a .................. to that math problem?

2. Natural sources cannot provide enough, energy to support this .................... world.

3. Do they know that we have ..................... cars? They don't need a driver.

4. Of all the ................... in the world, which one do you like best?

5. Playing outside is ............... healthy than staying inside.