Permanent linear change (PLC)measures the irreversible dimensional change of a refractory specimen after it is subjected to a high temperature for a specified duration. It is expressed as a percentage of the original length. This property helps evaluate the stability and thermal compatibility of refractory materials during service.
This is distinct from:
Modulus of rupture (A): a strength test under bending.
Modulus of elasticity (C): a measure of stiffness.
Pyrometric cone equivalent (D): a test for melting behavior.
Reference:
API Std 936 - Referencing ASTM C113 and C356 for permanent linear change testing procedures

The ASTM C704 standard requires the use of two specimens per sample for testing abrasion resistance:
"The abrasion resistance shall be determined using two 4½ in. × 4½ in. × 1 in. (114 mm × 114 mm × 25 mm) specimens per test sample."
- API Std 936, Section 6.4.4, Abrasion Resistance
This ensures accurate and reproducible results for quality control in refractory installations.

API 936 clearly designates responsibility for records:
"The contractor shall maintain records to document installation parameters and results. These records shall be complete, legible, and available for review."
- API Std 936, Section 9.3
The inspector may verify the accuracy but is not accountable for creating or maintaining them. Thus, Option C is correct.