The correct answer is: C. A gift was given to our colleague when she retired.
The sentence “Our colleague was given a gift when she retired” is in the passive voice. In the passive voice, the subject of the sentence is acted upon by the verb. In this case, the subject is “our colleague” and the verb is “was given.” The direct object of the sentence is “a gift.”
The other options are all in the active voice. In the active voice, the subject of the sentence performs the action of the verb. In these cases, the subjects are “our colleague,” “us,” and “we.” The direct objects of the sentences are “a gift,” “us,” and “our colleague.”
The passive voice is often used when the identity of the person or thing performing the action is not important or is unknown. In this case, the identity of the person or thing who gave the gift is not important. The important thing is that our colleague received a gift when she retired.
The active voice is often used when the identity of the person or thing performing the action is important. In these cases, the identity of the person or thing who gave the gift is important. The speaker may want to emphasize that they gave the gift, or that our colleague gave them the gift.