Correct option is (a) Timing gear
The best explanation: Timing gear is a combination of multiple gears where in one gear is mounted at one end of the camshaft and the other gear is mounted at the end of the crankshaft. In terms of size, Camshaft gear is bigger than the crankshaft gear and has twice as many teeth than crankshaft gear. For this reason, this gear is commonly called half time gear.