What would Aristotle's answer be to the opening of Plato's Meno: "Can you tell me Meno, can virtue be taught? Or is it not teachable but the result of practice, or is it neither of these, but men possess it by nature or in some other way?"
This is an excellent question. Some preliminary information is necessary to answer your question. First, the Greeks defined virtue (arete) as excellence. So, a virtuous builder would be an excellent builder. A virtuous person, then, is person who is excellent at being human. Second, for the Greek what characterizes the height of humanity is rationality. So, what it means to be excellent or virtuous is to live rationally.
In light of the above points, Aristotle believed that virtue could be learned through habit and effort. Based on this point, Aristotle believed that practice was necessary to be virtuous. This is how he would undoubtedly answer Plato. More specifically, Aristotle believed that virtue was the mean between deficiency and excess. So, if a person could learn and practice what this mean was in any area, then he or she could be virtuous.
Here is one example. If we are dealing with courage, then excess would be rashness and deficiency would be cowardice. Practice and habit (within in a community) in time would produce virtue.