Elephants are the only mammals that cannot jump.
Why it is true
Due to their colossal weight and the structure of their legs, which act as pillars to support their mass, elephants lack the anatomy necessary to lift all four feet off the ground simultaneously.
Source: Zoology
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.