Read the following text: while fda investigates all reports to the best of its ability, it does not always have access to all the information needed to determine the cause of the event. challenges include the following: incorrect, incomplete reports, often lacking contact information, which make following up with the complainant difficult or impossible; variability among the completeness of the reports (some reports may consist only of a single sentence with little detail.); reports that list the brand, but do not identify the specific product; absence of or lack of fda access to other information related to the report, such as medical records and medical histories. (in fact, some state medical privacy laws prevent fda from obtaining medical records related to the adverse event report.) complicating factors in determining the cause of a medical problem can include use of other supplements or medications at the same time; pre-existing or undiagnosed medical conditions; improper use of the product. source: u. s. food and drug administration:which line from this text is the topic sentence?