Context: Read the passage. Then answer the question.

Alpheid shrimp are small crustaceans that build burrows, or underground shelters, in the sand. Alpheid shrimp are blind and are vulnerable to predators when they are outside of their burrows.
A shrimp can share its burrow with a fish called a goby. The goby acts as a lookout for the blind shrimp. When the shrimp leaves the safety of the burrow, it touches its antennae to the goby's tail. If a predator comes near, the goby flicks its tail, alerting the shrimp to the danger. Both animals then retreat to the safety of the burrow.
Figure: a goby and an alpheid shrimp at the entrance of a burrow.
Which type of relationship is formed when an alpheid shrimp shares its burrow with a goby?
A. commensal
B. parasitic
C. mutualistic
From the given choices, pick the correct answer and respond by indicating the letter of the correct option.
Answer: C