On a Hike in the Mountains, You Find a Stream

On a hike in the mountains, you find a stream with a rocky bottom. Many of the rocks are covered in algae. Which type of mollusc is most likely to be found living in this environment?

A) A cephalopod because it can move quickly through the stream to avoid predators.
B) A gastropod because it can use its radula to scrape the rocks for algae on which to feed.
C) A bivalve because its sedentary life style allows it to remain still when currents flow over the rocks.