Complete the sentence: Firefighters had ___ put out the fire.

• A. Been able
• B. Been unable
• C. Are able
• D. Was unable

Answer: (B)

This question tests how to express past inability using the perfect tense with a to-infinitive. After had, we use been able to or been unable to to show what someone was able or unable to do up to a certain past moment.

The best completion is been unable because it fits the past perfect structure: had been unable to put out the fire. This means, by that past time, the firefighters had not managed to put it out. The other options break grammar or tense: been able would need to include to (had been able to put out) and would imply success; are able is present tense; was unable mismatches the plural subject and the past-perfect construction.