The correct answer is: B. A fox was caught by the tiger.
The verb “catch” is a transitive verb, which means that it requires a direct object. In this case, the direct object is “fox.” The tense of the verb is simple past, which indicates that the action of catching took place at a specific point in time in the past. The sentence could be paraphrased as “The tiger caught the fox at some point in the past.”
The other options are incorrect because they use different tenses or do not have a direct object. Option A, “A fox has been caught by the tiger,” uses the present perfect tense, which indicates that the action of catching has been completed but has some relevance to the present. Option C, “A fox is caught by the tiger,” uses the present tense, which indicates that the action of catching is happening now. Option D, “A fox had been caught by the tiger,” uses the past perfect tense, which indicates that the action of catching was completed before some other action in the past.
In conclusion, the correct answer is: B. A fox was caught by the tiger.