Python Question

The answer is C but I am unsure how to find that answer

Any help greatly appreciated

Question 2 def notSubStr (a, b) for i in range (1, len(b)+1): sub b[:1] if sub not in a return sub return a wordo'ads' word! ' ado ' print(notSubStr (wordo, word1)) a) ''(the empty string) b) ad c) ado d) ads e) none of the above