similar vs the same

The twin looks _____ each other. It’s difficult to tell ____.
A. similar to, which is which B. same as, who is who
C. similar to, who is who D. the same to, which is which
In my opinion, A should be right. Similar to indicate that they are almost the same while the same means that two things are identical. I am not sure about the second one, “which is which” seems better but I have little to prove myself.
What is your take on this one?

My take, “C”.

No correct answer is provided for the first sentence, which should either be:
The twins look similar to each other.
The twins look the same as each other.
The twin looks the same as his sibling.
The twin looks similar to his sibling.

The same as = identical similar to = almost identical. Either of these is correct.

It’s difficult to tell which is which (that is, which twin is which).
‘Who is who’ would not usually be used in this context, unless just before this sentence, the twins were asked about using their names:
What do you think of John?
Which one is John? The twins look so similar to each other that its difficult to tell who’s who. (that is, Who is John(this person) and who is James(that person))