What is the independent variable in farmer browns experiments

In this case, the statement that people who exercise for an hour may have lower cholesterol levels is .

Match each description to the appropriate biome. tropical savanna desert tropical rain forest taiga tundra has sparse vegetation and very cold temperatures located near the equator and contains trees that form dense canopy layers is very hot and dry, and has plants that need little water has cold winters, heavy snowfall and is dominated by conifers has warm temperatures and is dominated by grasses

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?