Ahuman activity that could significantly decrease
the amount of carbon dioxide in the air is
(1) increasing the use of fossil fuel
(2) controlling insect pests that eat stored grain
(3) burning garbage and trash to generate
electricity
(4) preserving and expanding forest habitats that
shelter wildlife

the answer is:

carbon dioxide

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.