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

The door was opened by the children for their father.

The children opened the door for their father.

The correct active voice of the given sentence is The children opened the door for their father.

The passive voice of the sentence is The door was opened by the children for their father. 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 "the door" and the main verb is "open." The past participle of "open" is "opened." So, the passive form of the sentence is The door was opened by the children for their father.

The active voice of the sentence is formed by putting the subject of the passive sentence before the verb and removing the verb "to be." In this case, the subject of the passive sentence is "the children" and the main verb is "open." So, the active form of the sentence is The children opened the door for their father.

The other options are incorrect because:

• The children was opened the door for their father. is grammatically incorrect. The subject of the sentence is "the children," which is plural. The verb "was" is singular.
• The children are opens the door for their father. is grammatically incorrect. The verb "are" is present tense, while the original sentence is in the past tense.
• The children opens the door for their father. is grammatically incorrect. The verb "opens" is present tense, while the original sentence is in the past tense.