D. Make the two groups live in different climates.
Separating the fruit fly population into two groups living in different climates would most likely increase the rate of speciation. This is because the two groups would experience different selective pressures in their respective environments, which could lead to genetic divergence over time. As they adapt to their different environments, they may develop unique characteristics that make interbreeding between the groups less likely or even impossible, resulting in the formation of two distinct species.
~~~Harsha~~~