How does mario know his pet likes his new bed?
a.
his pet makes himself comfortable.
b.
his pet sings.
c.
his pet goes to sleep.
d.
his pet waves his antennae.

I think all of the above     

C. 
Reasoning: A: you can make yourself comfortable anywhere
B: I doubt that the animal could sing, but even if he could that does not indicate enjoying the bed
C: Sleeps, is comfortable
D His pet waves his antennae? Antennae don't usually indicate happiness, cockroaches use them as sensors.