Human noses can distinguish over 1 trillion scents.
Why it is true
Contrary to the old myth that we can only smell 10,000 scents, our olfactory receptors are incredibly powerful and sensitive.
Source: Neuroscience
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.