Which one of the following is not the correct statement with respect to the involute profile toothed gears in mesh?

• A. Pressure angle remains constant from the start till the end of the engagement.
• B. The base circle diameter and the pitch circle diameter of the two mating involutes are proportional.
• C. When two involutes are in mesh, the angular velocity ratio is proportional to the size of the base circles.
• D. The shape of the involute profile depends only on the dimensions of the base circle.