Correct option is C
Crowning is the removal of a slight amount of tooth from the center on out to reach the edge, making the tooth surface slightly convex. This method allows the gear to maintain contact in the central region of the tooth and permits avoidance of edge contact with consequent lower load capacity. Crowning also allows a greater tolerance in the misalignment of gears in their assembly, maintaining central contact.
Backlash is the difference between the tooth space and the tooth thickness, as measured on the pitch circle. Face width is the width of the gear tooth measured parallel to its axis. Working depth is radial distance from the addendum circle to the clearance circle. It is equal to the sum of the addendum of the two meshing gears.
