Which of the following statements best describes how science has developed
 over time?
 A. Worldwide, scientists work independently to build the scientific
 knowledge within their own countries. 
 B. All useful scientific knowledge has been developed within the past
 100 years.
 C. Until 50 years ago, only men made contributions to scientific
 knowledge.
 D. Men and women all over the world have investigated scientific
 questions throughout history.