The scientists could hear the howling coyotes.

It starts with a few falsetto yips, then blossoms into something resembling maniacal laughter, the yips stringing together into chattering howls. It's an attention-grabbing sound, and an eerie one: coyotes howling, usually in the evening or at night, a chorus that is being heard with increasing frequency throughout the Northeast—and not just in remote wilderness areas, but in towns, suburbs, and city fringes.

Explanation:

and that is why

answers

a. nitrogen (n)

d. oxygen (o)

hope it

none because it's so obvious