The dependant variable would be the salmon, because they depend on the water and pollution levels to give a result.
Vertebrates have a bilateral symmetry due to which their entire body is divided into right and left halves while the invertebrates either have radial symmetry or the bilateral symmetry. Therefore, option D is correct.
The other basic differences between the vertebrates and the invertebrates are that vertebrates have a spinal cord and a backbone while invertebrates lack them, vertebrates have well developed brain, lungs or gills in respiratory system and closed circulatory system.
Dead zones are low-oxygen<span>, or hypoxic, areas in the world's oceans and lakes
(answer is dead zones)</span>
