As shown in the figure, one end of the light spring is connected with the object block P, and the other end is fixed on the board. First, place the board horizontally, and make the spring in the stretching state. Slowly lift the right end of the board, so that the inclination angle increases gradually, until the object block P is just about to slide down along the board. In this process, the change of static friction force on the object block P is () A. First decrease and then increase B. first increase and then decrease C. increase all the time D. remain unchanged

As shown in the figure, one end of the light spring is connected with the object block P, and the other end is fixed on the board. First, place the board horizontally, and make the spring in the stretching state. Slowly lift the right end of the board, so that the inclination angle increases gradually, until the object block P is just about to slide down along the board. In this process, the change of static friction force on the object block P is () A. First decrease and then increase B. first increase and then decrease C. increase all the time D. remain unchanged

Let G be the gravity of the block, θ be the angle between the board and the horizontal plane, f be the elastic force of the spring, f be the static friction force