You are underway at 5 knots and see on

You are underway at 5 knots and see on your radar a contact 10 miles directly astern of you. 12 minutes later，the contact is 8 miles directly astern of you. What is the estimated speed of the contact? （）

• ADead in the water
• B1 knot
• C10 knots
• D15 knot