One of my . ..... is a lecturer in the university.
Answer Details
The correct answer is "sisters". The sentence is referring to more than one sister. To make the noun "sister" plural, the letter "s" must be added to the end of the word. Since the sentence is indicating that only one of the sisters is a lecturer in the university, the apostrophe and the letter "s" must be added after "sisters" to show possession. Therefore, the complete sentence should read: "One of my sisters is a lecturer in the university."