Answer: a. forests
A biomass can be defined as the quantity or amount of living matter available in a given habitat. The living matter refers to the number of animals, plants and microbes present in a location that interact with each other in a food chain. The forest cover of the earth is 31% it includes diversity of living organisms not found in an other biome such as oceans, grasslands and deserts. Forests are ideal habitat that provide resources like water, shelter, food, mates and others that supports the existence of large number of lives. Therefore, Seventy-five percent of the Earth’s biomass is contained in forests.