My sister was bitten by a dog last month. (to bite)

Your sentence, "My sister was bitten by a dog last month," is in the passive voice, and the verb tense is past simple. If you're asking about how to form the active voice for this sentence, it would be:

"The dog bit my sister last month."

In this case, the verb "to bite" is in the past tense "bit" in the active voice.

If you want to use a different form of the verb "to bite" in other tenses, you would structure it as follows:

1. Present Simple (active): "The dog bites my sister."

2. Present Continuous (active): "The dog is biting my sister."

3. Future Simple (active): "The dog will bite my sister."

4. Past Perfect (active): "The dog had bitten my sister."

5. Present Perfect (active): "The dog has bitten my sister."

The sentence you provided is correctly formed in the passive voice, where the focus is on what happened to your sister, not on the dog doing the action.