Select the correct passive form of the given sentence.

They offered me a chair

I was offered a chair by them.

The correct passive form of the given sentence is I was offered a chair by them.

The active voice of the sentence is They offered me a chair. This sentence is in the simple past tense, which is used to describe an action that happened in the past. The passive voice of the sentence is formed by putting the subject of the active sentence after the verb "to be" and the past participle of the main verb. In this case, the subject of the active sentence is "they" and the main verb is "offer." The past participle of "offer" is "offered." So, the passive form of the sentence is I was offered a chair by them.

The other options are incorrect because:

• A chair is offered to me by them. is in the present tense, while the original sentence is in the simple past tense.
• A chair was being offered to me. is in the past progressive tense, which is used to describe an action that was happening in the past but is not happening anymore. The action of offering me a chair is still happening, so the past progressive tense is not the correct tense to use.
• I offered a chair to them. is the active voice of the sentence, while the question is asking for the passive voice.