Answer: d. an algae that grows on the surfaces of rocks.
Kelps are large brown algae seaweeds that grow along rocky shorelines so we choose d as an answer. Three types of Kelps are found mostly on the Pacific coast, Macrocystis (giant kelp), nereocystis luetkeana) and the Alaria fistulosa.
Kelps which are about 30 different genera, included species from Laminariales and Fucales.