Option a is correct
Brazil has high diversity because it is located near equator.Brazil is the Earth’s biodiversity champion. Between the Amazon rainforest and Mata Atlantica forest, the woody savana-like cerrado, the massive inland swamp known as the Pantanal, and a range of other terrestrial and aquatic ecosystems, Brazil leads the world in plant and amphibian species counts. It ranks second in mammals and amphibians, third in birds, reptiles and fish.
High biodiversity in an ecosystem means that there is a great variety of genes and species in that ecosystem. A great variety of genes and species means that the ecosystem is better able to carry out natural processes in the face of external stress.