How can a historian determine whether a claim is valid? make sure it is not a counterclaim determine if it shows a point of view evaluate the evidence used to support it apply her own biases to interpret it

The correct answer is Evaluate the evidence used to support it

They need to examine how valid the evidence is and whether  there's bias in the claim as well as in the evidence. As long as these terms are fulfilled, a historic claim can be made valid. Other people can present counterclaims with their own evidence which is when they revise both claims and find what the actual truth is.