The use of straight or curved external gear teeth in mesh with internal teeth in gear and spline couplings is specifically employed accommodate
(a) torsional misalignment
(b) parallel misalignment
(c) angular misalignment
(d) substantial axial movements between shafts
The question was asked in an online quiz.
My enquiry is from Standard Spur Gears-1 topic in chapter Toothed Gearing & Gear Trains of Machine Kinematics