ANS:B - cold rolled mild

Keys are typically made of cold rolled mild steel bars. Cold rolling is a process that strengthens steel by compressing it at room temperature, resulting in improved mechanical properties such as hardness and strength. Cold rolled mild steel is well-suited for key applications because it offers good strength, hardness, and wear resistance, making it capable of withstanding shear and crushing forces without failing easily. Additionally, the cold rolling process produces a smooth surface finish, which is important for proper functioning and fitting of keys in machinery. Therefore, the correct choice from the given options is: cold rolled mild