Select the correct active form of the given sentence.

The strike has been called off by the workers.

The workers have called off the strike.

The correct active form of the given sentence is The workers have called off the strike.

The original sentence is in the passive voice, with the subject "the strike" and the verb "has been called off." The passive voice 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 "the workers" and the main verb is "call off." The past participle of "call off" is "called off." So, the passive form of the sentence is The strike has been called off by the workers.

The active form of the sentence puts the subject of the sentence, "the workers," before the verb "call off." The verb "call off" is followed by the direct object, "the strike."

The other options are incorrect because:

• The workers are calling off the strike. is in the present progressive tense, while the original sentence is in the present perfect tense.
• The workers had called off the strike. is in the past perfect tense, while the original sentence is in the present perfect tense.
• The strike has called off the workers. is grammatically incorrect. The subject of the sentence is "the strike," but the verb "has called off" is followed by the pronoun "the workers."
• The strike has called off. is in the present perfect tense, but it lacks a subject.