12. Ship A and B are sister ships. Wind force 20 knots and 10 knots were encountered by ship A and ship B respectively. How many times of forced was sustained by ship A compared by ship B?
(A) 2 times.
(B) 3 times.
(C) 4 times.
(D) 6 times.

F=(1/2)*mv^2雖然是叫wind...