Task: Question Answering
Input (English): Question: The sequence a1, a2, a3, a4. a5 is such that an = a n-1 +5 for 2≤ n ≤ 5. If a5 = 33 what is the value of a1 ?

 Option A: 1

 Option B: 6

 Option C: 13

 Option D: 16

 Option E: 21
Output (English): Option C