Secondary sources are valuable because offer corroborated evidence about important events. Thus the correct answer is A.
The sources which are not considered firsthand sources and derived information from other primary sources are referred to as secondary sources. These include reviews and criticisms made by scholars and so on.
The corroborated evidence signifies the presence of already existence information which is also utilised in secondary sources which do not affect the credentials or reliability of research.
Therefore, option A is appropriate.
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