The correct option is B; let’s look at the concept.

P) Engine block:

Due to the large complex shapes of the engine blocks, the most suitable manufacturing process is Casting. Usually, Sand Casting is used but die casting can also used it is more cost-effective as the die wear out easily due to the high temperature of the molten metal. The casted engine block is then machined to get the surface finish and coolant passages. So the correct match is (3).

Q) Brake Pads:

The friction parts like Brake Pads are usually produced by the Powder Metallurgy process.  They not only have obvious advantages in performance but also have great flexibility in product diversification. Using powder metallurgy technology can change the material components in a wide range, can avoid the loose, traditional manufacturing process of shrinkage, microstructure, and grain growth of dendrite segregation and other defects, thus improving parts of the mechanical properties and friction and wear properties.

The methodology used here is based on newly prepared sample materials that are subjected to a common constant sintering pressure but with three different sintering temperatures. These will then undergo various kinds of mechanical and tribological behavior tests before and after a thorough brake wear test to verify the rate of material loss which will help determine the wear-ability of materials. So the correct match is (4).

C) Connecting Rods:

A connecting rod is like a shaft connecting the piston to cranks in an engine. This is usually made by hot forging methods. Hot forged connecting rods, in particular forged connecting rods for an internal combustion engine, especially when they are made of steel, are manufactured by a process which comprises hot forging of a connecting rod rough forging, a heat treatment, and a machining operation.

These rods work in severe conditions and thus require good properties like strength. Hot forging causes the impact which usually downscales the grain size providing better strength properties. So the correct option is (1).

S) Door Panels:

Door panels used in cars or other places require good bending with a large bent radius. This can be attained by stretch sheet metal forming as the stretch formed parts are usually large and have a large bend radius.

Stretch forming is a metal forming process in which a piece of sheet metal is stretched and bent simultaneously over a die in order to form large contoured parts. Stretch forming is performed on a stretch press, in which a piece of sheet metal is securely gripped along its edges by gripping jaws. The gripping jaws are each attached to a carriage that is pulled by pneumatic or hydraulic force to stretch the sheet. The tooling used in this process is a stretch form block, called a form die, which is a solid contoured piece against which the sheet metal will be pressed. Horizontal stretch presses mount the form die sideways on a stationary press table, while the gripping jaws pull the sheet horizontally around the form die.