A scientist observes previously unexplained curved lines etched in rocks in the Negev Desert.
Which creative method below would explain how the scientist discovered that snails were carving the lines each night as they feed on lichens that grew on the rocks?

A. The scientist moved a rock into the laboratory to study its composition.

B. The scientist found rocks of similar sizes in other locations.

C. The scientist researched in the library to discover if other rocks had similar lines.

D. The scientist gathered empirical evidence by recording a video of what happened on the rocks 24 hours a day.