A. Pull the wooden block horizontally with a spring dynamometer. Pull the block horizontally to the right, slide horizontally to the left, and the block moves in a straight line at a constant speed. Sliding friction and tension are a pair of balancing forces. This statement is correct and does not conform to the meaning of the question.

B, the relationship between sliding friction and contact area can be explored by controlling the pressure of the wood block and the roughness of the contact surface, making the wood block flat, horizontal and vertical, and changing the contact area. This statement is correct and does not conform to the meaning of the question.

C. When the spring dynamometer pulls the wood block to accelerate, the pressure, roughness of contact surface and sliding friction force remain unchanged. This statement is wrong and in line with the meaning of the question.

D. When the spring dynamometer pulls the wood block to do accelerated motion, the motion speed of the wood block increases and the motion state changes constantly. This statement is correct and does not conform to the meaning of the question.

So choose C.