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The correct answer regarding the number of datums that can be specified in a feature control frame is three. In geometric dimensioning and tolerancing (GD&T), a feature control frame is a rectangular box that contains the geometric tolerance, the related datum references, and any modifiers that apply.

A single feature control frame can reference up to three datums, which can be sequentially arranged to establish a reference coordinate system for the designed part. This is critical in manufacturing and inspection processes, as it ensures that features of a part are measured consistently and precisely in three-dimensional space.

Referencing more than three datums in a single feature control frame is not standard practice, as it can lead to confusion and complexity in interpreting the tolerances. Therefore, specifying up to three datums maximizes efficiency and clarity in the design and manufacturing process.