The correct answer is A. Cast steel.
Cast steel is a type of steel that is made by melting iron and then pouring it into a mold. The molten steel cools and hardens in the mold, taking the shape of the mold. Cast steel is a strong and durable material that is often used to make high-grade instruments.
Bessemer steel is a type of steel that is made by a process called the Bessemer process. The Bessemer process is a refining process that removes impurities from molten iron. Bessemer steel is a strong and durable material that is often used to make structural steel.
Mild steel is a type of steel that is made by adding a small amount of carbon to iron. Mild steel is a relatively soft and ductile material that is often used to make sheet metal and other products that require a lot of bending and forming.
Whitworth compressed steel is a type of steel that is made by a process called the Whitworth process. The Whitworth process is a manufacturing process that uses a series of dies to compress steel rods into smaller and smaller diameters. Whitworth compressed steel is a strong and durable material that is often used to make machine parts.
In conclusion, the correct answer is A. Cast steel. Cast steel is a strong and durable material that is often used to make high-grade instruments.