TOEFL Reading: ETS-TOEFL阅读机经 - S1M190366BA7KWHCL$

According to paragraph 6, environmental forces limit the power of natural selection in which of the following ways? A. They change the reproductive process in significant ways. B. They destroy potentially favorable gene combinations before they can be selected. C. They interfere with the transmission of chromosomes from parent to offspring. D. They weaken the ability of individuals to maintain high fitness levels.