Which principle allows an insurer to predict losses with greater accuracy as the number of similar exposure units pooled together increases?

Why this is the answer

Insurance is built on risk pooling: a single death is unpredictable, but the death rate among 100,000 forty-year-old nonsmokers is highly predictable from mortality tables. The law of large numbers is the statistical principle that makes this work — as the number of independent, similar exposure units increases, the observed loss frequency approaches the expected frequency. Adverse selection is the opposite problem (worse risks crowd in), indemnity is the make-whole principle of property insurance, and subrogation is the insurer's right to recover from a liable third party. Per the Florida Agent's Health & Life Exam Content Outline §IV.