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    Crocodiles are often confused with alligators, but there are some easy-to-spot differences. An alligator's jaw is U-shaped, while a crocodile has a V-shaped jaw, according to the San Diego Zoo, Crocodiles also have teeth that stick up over their upper lip when their mouths are closed.

    Another difference between alligators and crocodiles is that crocs have salt glands on their tongues. These modified salivary glands help crocs tolerate living in salt water. Alligators and caimans have lost the ability to secrete excess salt through the tongue glands and therefore, they prefer to live in fresh water areas.

Common people are difficult to differentiate whether the reptile is a crocodile ____ an alligator.

Which best completes the sentence?