The correct answer is D. A newspaper article titled "Number of Concussions in Counties With and Without Helmet Laws"
Step-by-step explanation:
In research, which is the process of solving a problem or question, the word source refers to documents or similar materials such as books, articles or even websites where you can information about the topic the research question is about. This means the source should provide information to answer the question proposed or at least clarify one section of it. In this case the research question is "Have helmet laws decreased the number of childhood head injuries?" which means the author of this research process needs a source that shows the effect of helmet laws have in terms of the number of childhood head injuries or that clarify whether this type of laws can decrease or increase these type of injuries. Because of this, the most helpful source for answering this question is "A newspaper article titled "Number of Concussions in Counties With and Without Helmet Laws" as this will provide information about the number of injuries in areas with helmet laws in comparison to those without helmet law, which is exactly the type of information required for answering the research question proposed.