A basketball with a gravity of 5N is thrown vertically. It is assumed that the resistance of air to the basketball is 0.5N, Then the resultant forces of the basketball in the process of vertical rising and falling are (10N / kg) A.5.5N,5N B.5.5N,4.5N C.4.5N,5.5N D.5N,4.5N

Answer: B
analysis:
When the ball flies upward, the air resistance is downward and the gravity is also downward. The sum of the two forces is 5 + 0.5 = 5.5n, and the resultant force is downward;
When the ball flies downward, the air resistance is upward, the gravity is downward, the two forces are subtracted: 5-0.5 = 4.5n, and the resultant force is downward

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