Can anyone tell me which function is not working and its reason?

Exercise 3: Given 3 int values, a b c, return their sum. However, if one of the values is the same as another of the values, it does not count towards the sum. For example: lone_sum (3, 2, 3) returns a value of 2. A) def lone sum (a, b, c): sum a + b + c if a == b and b == C: def lone sum (a, b, c): sum + b + c if a == b and b == sum 0 elif a == bor a == C: return 0 if a b: sum = sum (2 * a) sum elif b C: if a sum sum (2 * b) sum b return sum if b == C: sum a return sum B) def lone_sum (a, b, c): b and b == C: if a == if a sum 0 D) def lone sum (a, b, c): sum = a + b + c == b and b == C: sum sum (a + b + c) elif a bor a == C: sum sum (a + a) elif b == C: sum sum - (c + c) elif a == b and b != C: == sum elif a C and a != b: sum = b elif b == c and b != a: sum = a return sum else: sum a + b + c return sum