It's about the size of a small slim upside down goat, if you can imagine such a thing.The sloth really is not only one of the laziest, but one of the strangest of the strangest of mammals.It spends most of its life asleep.But even when it's awake, it only moves very slowly.  There are two main kinds defined by the number of toes that they have on their font legs.It's the three-toed which has really slothful habits, and the one that interests me most.You're not likely to have seen it in zoos, for unlike the two-toed which will rat all kinds of vegetables and fruits,, the three-toed is really picky and will only accept leaves and fruits of a few particular kinds, which few zoos can supply.And in any case, it doesn't make an exactly fascinating exhibit, since it spends most of its tile sleeping. When the skins and skeletons of this extraordinary beast reaches Europe, artists given the task of illustrating the species in natural history books, showed it standing upright on its four thin legs, even though thee hooks on its feet and the fur on its body all pointed very obviously in what you might call the wrong way.After all, the artists must have said to themselves, it would be too ridiculous to show it as animal that spent all its life upside down. Sloths are only capable of a faint wheeze and occasional whistle.These sounds are probably only made to deter a meat-eater like a lion, and certainly not to communicate with one another, for sloths are virtually stone deaf.It's said that an enthusiastic zoologist investigating the hearing ability of sloths fired his gun close to  _ .It slowly raised its head, blinked at the scientist, and then went back to sleep again. Which of the following word best describes a sloth?
unimaginable unfaithful inactive endangered