Get a IEnumerable<T> from a IEnumerable<IEnumerable<T>>

public class Item { ... }

public class Order
{
    public List<Item> Items
    ...
}

public class Customer
{
    public List<Order> Orders
    ...
}

Now, using LINQ I need to get all items that a customer bought. How can I?

I tried something like var items = from o in cust.Orders select o.Items; but result is IEnuberable<List<Item>> and I wanna just one IEnumerable<Item>.

I'm asking here to try to avoid coding 2 loops.