My uncle promised me a present.

Active voice: "My uncle promised me a present."

In this sentence: "My uncle" is the subject, "me" is the indirect object, and "a present" is the direct object.

To convert it into passive voice, we can make either the indirect object or the direct object the subject of the passive sentence.

Option B correctly changes "me" (indirect object) into the subject: "I was promised a present by my uncle."

This structure is grammatically correct and natural in English.

Why the other options are incorrect:

Option A: "A present was promised by my uncle to me" is grammatically correct but less natural in common usage.

Option C: "I had been promised" uses past perfect tense, which does not match the original simple past tense "promised".

Option D: "I was promised by my uncle a present" is grammatically awkward and not the standard structure.

Therefore, Option B is the best and most appropriate passive voice transformation.