Answer: d. rule 26
Explanation:
An expert witness has technical knowledge or education that adds credibility to a testimony or an argument in a civil proceeding. While there are other sources for providing this technical know-how, using an expert witness is more common.
Rule 26 of the Federal Rules of Civil Procedure defines the conditions under which such a witness can be introduced into the proceeding. The name and contact details of the expert witness must be provided. Also, a copy of all the documents that may be used to support a claim or defense must be provided.