Amazon.com Inc. is evaluating two investment options for its fulfillment centers:

2. 
   
   • Option A requires an initial investment of $500 million and generates annual cash flows of $150 million for the next five years.
   • Option B requires an initial investment of $600 million and generates annual cash flows of $180 million for the next six years. If Amazon's required rate of return is 12%, which option should they choose based on the net present value method?