In the walls of the heart, two layers of tissue form a sandwich around a thick layer of muscle called the .

the answer is c.mitochondria. glad to .

answer: 20 percent

the fish culture has become a developing commercial practice in developing countries which is already prominent in developed countries of the world. the major fish protein demand is being supplemented in developing countries is   fishing to meet the needs of the growing population. therefore, in some developing nations, the percentage of animal protein from fish in the diet can be as high as 20 percent.