finding the index of the elements appended to new list from its old list - python 2

I have two lists (A and B) with some common elements in between them. I want to create a new list (C) with all the common elements from A that are also in B, as well have the index of where the elements was originally in A.

The two lists are as fallows,

A=[[[a, b], [c, d]],
   [[e, f], [f, t]],
   [[a, b], [c, d]],
   [[g, h], [t, r]]]
B=[[[a, b], [c, d]],
   [[g, h], [t, r]]]

The code Im using to find the common elements are as fallows,

C=[[ ]]
for i in range(len(A)):
    if A[i] in B:
        C[0].append(A[i])

The output is perfect, except I'd like to add in the index of the elements in C from where there come from in A (even if there are duplicates), possible besides each elements or even in a new list, although Im not sure the code that would do that, so any help is appreciated.