What is the book or excerpt?
Active voice is a sentence form wherein the action, represented by the verb, is done by the subject. Therefore, the sentence that is written in the active voice is, option B. Scientists found a perfectly preserved woolly mammoth frozen in ice. The subject in the sentence is the word "scientists" and the action word "found" is done by the subject.
Either 2 or 4. I’m leaning closer to 4 though. My answer would be 4.