Concept:After the phrase “one of,” use a plural noun because it refers to a single member selected from a group.
Explanation:The structure “one of my…” always requires a plural noun after it.
So, the correct form is “one of my sisters,” meaning one sister out of many sisters.
Option A, “sister,” is wrong because it is singular and cannot follow “one of.”
Option B, “sister's,” is a possessive singular form, which does not fit the meaning here.
Option D, “sisters’,” is a possessive plural form, but the sentence needs no possession.
Only option C, “sisters,” creates the correct phrase: “One of my sisters is a lecturer.”
The verb “is” then correctly agrees with the singular subject “one.”
Answer:C. sisters