The correct answer is A. tropical rain forest.
Tropical rain forests are the most productive ecosystems on Earth. They have a high annual rainfall, warm temperatures, and abundant sunlight. This combination of factors allows plants to grow quickly and produce a lot of biomass.
Temperate grasslands have a moderate climate with warm summers and cool winters. They receive less rainfall than tropical rain forests, but more than deserts. This allows plants to grow, but not as quickly as in tropical rain forests.
Deserts have very low rainfall and high temperatures. This makes it difficult for plants to grow, and they produce very little biomass.
Tundras are cold, dry ecosystems with short growing seasons. They receive very little rainfall, and the soil is often frozen. This makes it difficult for plants to grow, and they produce very little biomass.
In conclusion, tropical rain forests are the most productive ecosystems on Earth. They have a high annual rainfall, warm temperatures, and abundant sunlight. This combination of factors allows plants to grow quickly and produce a lot of biomass.