OG详解-OG3 文法 Q14

Choice A is the best answer. The sentence effectively emphasizes the aim, or goal, of the research study (in other words, what the researchers hoped to learn from the study): Rogers and Russell wanted to know if woodland expansion is related to changes in climate. 
Choice B is incorrect. The sentence emphasizes the researchers’ findings; it doesn’t emphasize the aim of the study. Choice C is incorrect. The sentence emphasizes the results of the study; it doesn’t emphasize the aim. Choice D is incorrect. The sentence emphasizes the methodology of the study; it doesn’t emphasize the aim.