For high grade instruments the steel preferred to, is

ANS:A - cast steel

Steel castings are used for a variety of reasons. They are mainly used when other types of cast irons do not have enough strength or shock resistance. Steel's physical properties allow the castings to be both strong and ductile. Cast steel usually refers to normal carbon steel and alloy steel, or called steel casting with carbon content lower than 2%.
Therefore, no big difference considering from the chemical content and raw materials for cast iron vs cast steel.