About one million Earths could fit inside the Sun.
Why it is true
The star at the centre of our solar system is so massive that its volume is overwhelmingly larger than that of all the planets combined, containing ninety-nine percent of the system's mass.
Source: Solar System
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.