Which of the following features does not improve the rate of diffusion?
a. thin membranes lining respiratory organs such as gills and lungs
b. multiple infoldings of respiratory surfaces, such as lamellae in gills
c. inhaled fresh air is mixed with old air from the previous breathing cycle
d. blood circulates in counter current direction to water flow in gills

not sure if this is what you'r looking for nnew= nold

not: both offer magnification to the atomic level.

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.