How to instantiate a GameObject from a .prefab file in C#?

Question

Unity

There is a .prefab file, how can I instantiate it?
For example, prefabs in Resources can be instantiated using the function:

UnityEngine.Object.Instantiate((GameObject)(Resources.Load(string.Concat("prefabs/game/civilianZombie_1"))));

However, this function takes a GameObject as one of its parameters, how can I create a GameObject variable that contains my prefab from the .prefab file?