What is a common requirement for a witness to provide testimony in court?

A common requirement for a witness to provide testimony in court is their presence at the crime scene. This is critical because a witness must have firsthand knowledge of the events they are testifying about, which typically comes from witnessing the incident or being in the immediate vicinity when it occurred. The credibility of a witness's testimony often hinges on their direct experiences related to the case, making their physical presence at the scene essential to support their statements with factual accounts.

In contrast, the other options don't necessarily apply to all witnesses. For example, a witness does not need to interpret laws; that role is typically fulfilled by attorneys or judges. Additionally, while certifications and expertise might be relevant for expert witnesses, they are not a requirement for general witnesses who can provide firsthand accounts. Lastly, having a legal background is not a prerequisite for providing testimony; witnesses from various backgrounds can testify based on their observations. Therefore, the most pertinent requirement listed is the witness's presence at the crime scene.