Which document ensures clear documentation of property interests in the land titles system?

The correct answer is C. Parcel register.

In the land titles system, the parcel register is the document that ensures clear documentation of property interests. The parcel register contains important information regarding the property, such as ownership details, legal description, encumbrances, and any interests registered against the property. This document is crucial for providing a complete and accurate record of the property's ownership and any associated interests that may affect it.

The other options (A. Abstract book, B. Deed register, D. Title book, E. Transaction log, F. Valuation record) do not serve the same purpose as the parcel register in documenting property interests within the land titles system. Each of these options may have relevance in real estate transactions or property management, but they do not specifically serve the function of providing clear documentation of property interests in the land titles system like the parcel register does.