Answer :
Final answer:
The ASTM specification number for ferrous metals begins with the letter A, marking it as a designation for this category of metals.
Explanation:
The ASTM designation system for ferrous metals is identified by looking at the prefix to the specification number. The correct way to identify an ASTM specification number for ferrous metals is by confirming that the number begins with the letter A. This indicates that the material in question falls under the category of ferrous metals according to ASTM standards. For example, A36 is a common ASTM specification for carbon structural steel. The use of the letter 'A' distinguishes this specification from those of non-ferrous metals, plastics, or other materials, each of which has its own unique alphabet prefix according to the ASTM coding system.