Final answer:
The characteristic common to both the Pampas and Llanos is grassy plains.
Step-by-step explanation:
The characteristic that is common to both the Pampas and Llanos is grassy plains. Both the Pampas and Llanos are expansive grassland regions located in South America. The Pampas are found in Argentina, Uruguay, and southern Brazil, while the Llanos are found in Venezuela and Colombia.