Which sentences are written in passive voice?
1. my little sister found three seashells in the tidal pool.
2. that book was written by one of my favorite authors.
3.sebastian and akiko are traveling to ohio this summer.
4. the contestants will be judged on style and originality.
5. in my house, fruit is often served after a meal.

Sentences 2, 4 and 5 are written in passive voice.

Explanation:

We use passive voice when we want to put an emphasis on the action and the object, rather than subject. In other words, subject is either insignificant in that particular case, or we do not know who/what the subject is. The object from the active sentence becomes the subject in the passive sentence.

For example, active sentence is: One of my favorite authors wrote that book, while passive sentence is: That book was written by one of my favorite authors.

We form passive from the auxiliary verb (often verb to be) and past participle.

i guess you are missing the idea that has to be supported, am i right?

a simple sentence must have at least one dependent clause.