True ... a triode.And trans-parent would be a valve
I don't know. If the Spartans were in "our time" they would have access to the weapons of war in "our time." In such case, I think Thermopylae pass would be defended as well today. There were five major battles at Thermopylae from the Spartan battle to WWII.Spartans couldn't have defended it if the battle were held in our times.