Options are:
a). chemical reaction.
b). eating quietly.
c). vibrating quickly.
d). being silent.
e). chemical changes.
f). hormones.
g). barks and snarls.
h). chemical messengers.

Fact 1: Sound can be used for communication by animals. Fact 2: Snarls and barks are the sounds they make. Given the two facts above, some animals communicate through what?
Answer:
g).