In the following question, a sentence is divided into four parts. Choose the part of the sentence which may contain a grammatical error in it. If all the parts of the sentence are grammatically correct and contextually meaningful, choose option “No error” as the answer choice.
She is (A)/ a dedicated officer (B)/ working in (C)/ an female unit. (D)

To identify the grammatical error, let us analyze the sentence piece by piece:
1. "She is" (A): This is grammatically correct. The singular subject pronoun "She" is paired with the correct singular present-tense verb "is".
2. "a dedicated officer" (B): This part is also grammatically correct. The indefinite article "a" correctly precedes the adjective "dedicated" (which begins with a consonant sound), modifying the singular noun "officer".
3. "working in" (C): This is correct. The present participle "working" functions as an adjective modifying "officer", followed by the preposition "in".
4. "an female unit." (D): This part contains a grammatical error. The indefinite article "an" is used before words that begin with a vowel sound. Since "female" begins with a consonant sound (/f/), the correct indefinite article to use is "a". The correct phrase should be "a female unit."

Therefore, the error is in part (D).