In the following passage, some words have been deleted. Fill in the blanks with the help of the alternatives given. Select the most appropriate option for each blank.

Snakes are elongated, legless, carnivorous 1. ______ that can be distinguished from legless lizards by 2. ______ lack of eyelids and external ears. 3. ______ species of snakes have skulls with several more joints than their lizard ancestors, 4. ______ them to swallow prey much larger than their heads with their highly mobile jaws. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side 5. ______ side, and most have only one functional lung.