The correct answer is B. tropical moist forests.
Tropical moist forests are the most biodiverse ecosystems on Earth, with an estimated 50% of all plant and animal species found in these forests. The high biodiversity of tropical moist forests is due to a number of factors, including the warm, humid climate, the abundance of sunlight, and the diversity of habitats found in these forests.
Temperate grasslands are found in regions with a moderate climate and receive moderate rainfall. These grasslands are home to a variety of plant and animal species, including grasses, herbs, shrubs, and small mammals.
Tundra regions are found in the Arctic and Antarctic regions. These regions are characterized by their cold climate, short growing season, and low precipitation. Tundra regions are home to a variety of plant and animal species, including mosses, lichens, and small mammals.
Hot deserts are found in regions with a hot, dry climate. These deserts are home to a variety of plant and animal species, including cacti, snakes, and lizards.
In conclusion, the greatest variety of animal and plant species is found in tropical moist forests.