How do I Aggregate multiple IEnumerables of T

Question

Given....

Public MasterList as IEnumerable(Of MasterItem)
Public Class MasterItem(Of T) 
    Public SubItems as IEnumerable(Of T)
End Class 

I

Answer 1

Are you looking for SelectMany()?

MasterList.SelectMany(master => master.SubItems)

Sorry for C#, don't know VB.