An involute pinion and gear are in mesh. If both have the same size of addendum, then there will be an interference between the
(a) tip of the gear tooth and flank of pinion
(b) tip of the pinion and flank of gear
(c) flanks of both gear and pinion
(d) tip of both gear and pinion
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This is a very interesting question from Minimum Number of Teeth on a Pinion for Involute Rack in Order to Avoid Interference topic in section Toothed Gearing & Gear Trains of Machine Kinematics