How do actin-based protrusions contribute to the protrusion step in cell crawling?

• A. They provide energy for the cell to move.
• B. They dissolve the extracellular matrix to clear a path for the cell.
• C. They signal other cells to move in the same direction.
• D. They extend the cell membrane forward, allowing the cell to reach out and attach to new surfaces.

Answer: (D)