Quiz: Two Unique Numbers

In 'Single Number III' (two numbers appear once, rest twice), after XORing all numbers you get $a \oplus b$. How do you separate $a$ and $b$?

1. A.Sort and scan for non-duplicates
2. B.Find a set bit in $a \oplus b$, partition numbers by that bit, XOR each group
3. C.Use a hash map
4. D.Divide by 2 repeatedly