An IEnumerable generic interface is returned from query expressions. A query expression that selects ints will be of type      Enumerable, IEnumerable<T> The only thing you want is to iterate over the elements in a collection. You only need read-only access to that collection.   IEnumerable  interface contains an abstract member function called  GetEnumerator()  and return an interface IEnumerator  on any success call. This  IEnumerator  interface will allow us to iterate through any custom collection.     any element in a collection can be retrieved through its index property. But instead of element index, the  IEnumerator  provides two abstract methods and a property to pull a particular element in a collection. And they are  Reset() ,  MoveNext()  and  Current .       IEnumerable can move forward only over a collection, it can’t move backward and between the items.       IEnumerable is best to query data from in-...