Many organisms that live in the rocky intertidal zone are adapted to cling to the rocks to withstand the a. pounding of the waves. b. changes in salinity. c. periods of being underwater and exposed to air. d. changes in density.

The correct option is POUNDING OF THE WAVES.
The intertidal zone in the marine aquatic environment refers to the regions of the foreshore and the seabed, which is exposed to the air at low tide and is submerged at high tide. The living organisms living in this zone are adapted to cling to the rocks in order to avoid been washed away by the waves.

The correct answer is a. we know this because n (hap) + n (hap) = 2n (dip).