Answer:
A) My sister, who just turned 18, is away at college.
Step-by-step explanation:
Options:
My sister, who just turned 18, is away at college.
My sister (who just turned 18) is away at college. (no comma's)
My sister-who just turned 18-is away at college. (no comma's)
My sister, is away, at college. (sentence should not have comma's in it)
Nonrestrictive components are groups of words that can be deleted from a phrase without altering the meaning of it. Nonrestrictive components can be separated from the remainder of the phrase since eliminating them does not affect the meaning.