Which synchronous modeling command can be used to merge cylindrical and conical split faces such as hole and boss geometry?

The command used to merge cylindrical and conical split faces, such as those found in hole and boss geometry, is "Merge Faces." This command is specifically designed to unify adjacent surfaces that can lead to a more simplified and cleaner geometry in your model.

In the context of synchronous modeling, merging faces is crucial for creating a single continuous surface from previously separate faces, which can be vital for downstream operations such as analysis, manufacturing, or aesthetic design. By using this command, you can effectively manage the complexity of the model and ensure that transitions between surfaces are smooth, which is particularly useful when dealing with various geometric features that interact with each other.

The other choices—Optimize Face, Combine Geometry, and Enhance Features—serve different purposes in terms of geometry manipulation. Optimize Face typically improves the quality or performance of the face without necessarily merging them. Combine Geometry focuses more on integrating different geometry types, while Enhance Features pertains to modifying existing features without primarily focusing on merging them. Therefore, for the specific task of merging split faces in cylindrical and conical shapes, "Merge Faces" is the most suitable command to use.