A rainbow is actually a full circle.
Why it is true
From the ground, we only see the upper half of a rainbow. From above, for example from an aeroplane or a mountain, it is possible to see the complete circle formed by the refraction and reflection of light in raindrops.
Source: NOAA
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.