Correct option is D
Sources, particularly in the context of historical and social science research, are more concrete and include accounts of eyewitnesses and personal letters. These sources provide tangible evidence that can be analyzed and interpreted to gain insights into past events, social dynamics, or individual perspectives. Eyewitness accounts and personal letters offer unique, firsthand perspectives that enrich our understanding of historical contexts, offering a depth and nuance that secondary sources may not capture. While sources strive for objectivity, the nature of personal narratives inherently includes subjective viewpoints, making critical evaluation essential. Not all sources are historical; contemporary sources are equally vital in studying current social, political, and cultural phenomena. This distinction highlights the diverse nature of sources and their role in constructing a comprehensive understanding of both past and present.