题目内容：
根据以下材料回答第 1～4 题：Passage One
“A rolling stone gathers no moss(苔藓)，”but there is one living animal that doesgather moss，the three-toed sloth(树獭)of South America．This slowest—moving memberof the animal kingdom is so inactive that moss actually gathers on its body and turns it green——strange as it seems!
Most of the sloth’8 life is spent motionless，hanging upside down frdm a limb．And
that is the way its hair grows．Long and coarse，the strands()from receptacles(花托)forthe damp j ungle algae(水藻)that turn the brown fur a mossy green．Actually this mosshelps the animal survive because it serves as a perfect camouflage against the leaf trees andhides the sloth from the jungle’s swift—moving hunters．The sloth would have little chanceof survival on the ground．With lon9，curved claws hooked over the limb of a leafy tree，itspends the long hot hours during the day drowsing and eatin9．Inch by inch，it strips theleafy limbs bare and crawls slowly down the trunk to find a new dining spot，but only at night．
In addition to looking rather like a vegetable，the sloth is a strict vegetarian．Running out of its favorite leaf is about the only thing that will make a sloth move．Then its apperite may even force the animal into swimming a stream to reach a juicy succulent(多汁的植物)．It will also force it into fighting to keep the tree all to itself．The sloth is lazy and prefers to be alone，but it will tolerate its own relatives !
A suitable title for this passage might be ．
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