The correct answer is D. Integrity. The phrase "contents are unchanged" directly refers to whether data has remained accurate, consistent, and unaltered. In security, integrity is the principle that protects data from unauthorized or accidental modification. Confidentiality is about keeping private data from unauthorized viewing. Authentication verifies identity. Availability ensures systems or data can be accessed when needed.
Only integrity matches checking that a downloaded file has not changed.
Exact Extract/Reference: The Tech+ Study Guide explains that integrity means "the data is accurate and consistent and from the indicated source," and identifies data integrity concerns such as unauthorized information alteration. The guide's summary also states that integrity is ensuring data is "true and correct."