Assign 'e' or '2' to the following double bonds based on their rankings at each end.
a) Bond A: Rank 1 - e, Rank 2 - 2
b) Bond B: Rank 1 - 2, Rank 2 - e
c) Bond C: Rank 1 - 2, Rank 2 - 2
d) Bond D: Rank 1 - e, Rank 2 - e