Some Major Changes That Occurred in Horse Body Size,foot Anatomy,and

Some major changes that occurred in horse body size,foot anatomy,and tooth morphology are hypothesized to be due to natural selection because

A) changes in global climates resulted in a shift from forest to grassland environments.
B) changes in global climates resulted in a shift from from grassland to forest environments.
C) decreasing body size led to higher reproductive success.
D) changing climates that caused altitudinal shifts in forest environments.
E) a mass extinction of their major predators.