Which of the following is a common role of an expert witness?

An expert witness plays a crucial role in legal proceedings by providing testimony that is based on specialized knowledge, skills, experience, or training in a particular field. This testimony is designed to help the court understand complex technical or scientific matters that fall outside the knowledge of an average juror. The expert witness can explain relevant concepts and facts that pertain to the case, which can include anything from forensic analysis to medical diagnoses to financial expertise. Their insights contribute significantly to the jury's understanding and can influence the outcome of the case by clarifying complex issues.

Other roles listed in the options do not align with the primary responsibilities of an expert witness. Presenting jury instructions is typically a role reserved for the judge. Making final rulings on cases is also the exclusive domain of the judge, who has the authority to decide legal conclusions based on the case before them. Assessing the credibility of other witnesses is often the purview of the jury, who evaluates the testimony provided during trial; although an expert may provide context, they do not typically take on this evaluative role regarding other witnesses.