Select the option that expresses the given sentence in passive voice.

The officers kept us waiting for one hour.

We were kept waiting for one hour by the officers.

The correct passive form of the sentence The officers kept us waiting for one hour is We were kept waiting for one hour by the officers.

The active voice of the sentence is The officers kept us waiting for one hour. 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 "us" and the main verb is "keep." The past participle of "keep" is "kept." So, the passive form of the sentence is We were kept waiting for one hour by the officers.

The other options are incorrect because:

• We kept waiting for one hour. is in the active voice.
• We keep waiting for one hour. is in the present tense, but the action of the officers keeping us waiting happened in the past.
• We are keeping waiting for one hour. is in the present progressive tense, which is used to describe an action that is happening now but is not finished. The sentence is describing an action that happened in the past, so the present progressive tense is not appropriate.