Answer: The answer to this question would be D.
Explanation: All of the given questions except D. "what size are the grains?" can help identify a rock formation. The age of the rock, geographic location, and environmental conditions can all provide important clues about the type and origin of the rock. Grain size, while a useful characteristic for describing the texture of a rock, may not be as useful for identifying a specific formation. Other characteristics such as mineral composition, color, and layering can be more informative for identifying rock formations.