The answer is long legs.
The traits that have higher chances of helping the organisms survive will most likely be the ones being passed on to the next generation. In this case, the lizards that have long legs are most successful in getting the food that they need compared to have short legs.
This case would fall on natural selection. Natural selection refers to the process by which an organism adapts and changes in response to its environment. It enhances the organism's traits to help them suit well in its environment to survive.