1. The Sun.

Dẫn chứng: Earth is the third closest planet to the Sun in the Solar system. 

2. The Blue Planet, or the Blue Marble are the other names for Earth.

Dẫn chứng:  It is also reffered to as the Blue Planet, or the Blue Marble because it's the only planet that has water in liquid from on the surface. 

3. Yes, it is.

Dẫn chứng:  Earth is the only planet that is capable of hosting any known form life. 

4. Scientists are looking for other planets to accommodate our increasing population.

Dẫn chứng: Scientists are looking for other planets to accommodate our increasing population.