Task: Question Answering
Input (English): Question: Which of the following is equal to 3^k*7^(k-1)?

 Option A: 3*21^(k-1

 Option B: 7*21^(k-1

 Option C: 21^k

 Option D: 3*21^k 

 Option E: 21^(2k-1
Output (English): Option A