Final answer:
NM cable must be installed at least 1-1/4" from the edge of wood studs to meet the National Electrical Code and prevent damage from nails or staples.
Step-by-step explanation:
When running NM cable through or on wood studs, the National Electrical Code (NEC) states that the cable must be placed at least 1-1/4" from the edge of a framing member where nails or screws are likely to penetrate. This is to prevent damage to the NM cable from nails or staples during the construction or after, as during the installation of drywall or other finishing materials.
C is the correct answer, which means the NM cable must be at least 1-1/4" from the face of the stud to prevent potential damage. This code requirement ensures safety and the integrity of the electrical system within the structure.