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One of the most difficult things for a human to face is the loss of a limb. If a person loses an arm or a leg, he/she must be fitted with an artificial limb. The situation is very different for a starfish. If a starfish loses an arm, it can grow a new one. ______ Snails can even regrow their heads-imagine what the world would be like if humans could do that.
(A) Scientists call this unidirectional regeneration. (B) Humans aren’t completely without regenerative talents. (C) The same thing happens for lobsters, salamanders, and many other animals. (D) When it comes to regeneration, few animals can equal the magic of the planarian. (E) This type of regeneration is demonstrated in a few animals, such as hydras and sea stars. (F) They hope that this line of research will make regeneration possible in humans someday.