The correct answer is C. A book published in 1970 by a soldier trained to protect elephants
Explanation:
In the case of historical sources or sources that describe events in the past, a source is considered as credible usually when it is a primary source which means the source was written by someone that experienced or witness the event studied. Additionally, the author of the source needs to be an expert on the area or someone related to the event and the source should provide information about the event studied. This implies in the case of looking for information about early efforts to stop elephant poaching a historical source or a source written in the past would provide this information, but this also needs to be written by someone that is an expert or is related to the event and therefore, the source with credible information is "A book published in 1970 by a soldier trained to protect elephants" because this address the topic that is being studied but also is credible because it was written by someone that directly participated in the efforts to stop poaching.
