Where a system is grounded, the grounded $($usually neutral$)$ conductor$($s$)$ in sizes $4$ AWG and larger must be identified generally by which of the following means?

a$.$ Continuous white or gray insulation along the entire length of the conductor

b$.$ Identification at the time of installation by a distinctive white or gray marking at the termination of the conductor; the marking must encircle the conductor

c$.$ Three continuous white or gray stripes on insulation other than green for the entire length of the conductor

d$.$ Any of the above