单项选择题A number of theories have been put forward about the possible causes of cancer.()
A. 理论上早巳预言了癌症的病因。B. 人们就造成癌症的病因提出了不少理论。C. 大量的理论已经用于解释引发癌症的原因。D. 人们已用大量理论来研究癌症的原因。
单项选择题Each person sees the same scene, but each perceives something different about it.