What FDA regulation defines the contents of an Investigator's Brochure?

21 CFR 312.23(a)(5) is the correct answer because it specifically states that the Investigator's Brochure must contain a summary of "significant human experience." B, C, and D are incorrect because they do not provide any specific requirements or information about the contents of an Investigator's Brochure. B references the requirements for submitting an IND application, C references general human subject protection regulations, and D refers to the duties of sponsors to provide information to investigators. None of these choices specify what needs to be included in the Investigator's Brochure, making them incorrect answers.