Considering the diagram below, which summarizes two signaling pathways initiated by activated GTPases of the Rho family, what letter (A to D) corresponds to each of the following? Your answer would be a four-letter string composed of letters A to D only, e.g. ABCD.

( ) Rac-GTP
( ) Rho-GTP
( ) Lamellipodia formation
( ) Stress-fiber formation