We can say that a sentence is in passive voice when the subject of the phrase is also the receptor of the action, in contrast with the active voice where the subject executes the action.
In the first paragraph the passive voice sentence is "Many fish are usually found by her", the subject is "many fish" but the action is done by "her" (Lily).
In the second paragraph the passive voice sentence is "Long walks are enjoyed by Shadow", notice that in the active form, the sentence would be "Shadow enjoys long walks" but in the passive form the subject is the object of the sentence, in this case "long walks".
In the third paragraph the passive voice sentence is "He was driven around town by a cab driver named Martin", again, Martin is the one who executes the action (driving John around town), so in the passive voice, the subject is "He" (who receives the action).
In the last paragraph the passive voice sentence is "The dolphins were fed and carefully handled by the trainers", The subject is "The dolphins" and they are receiving the action (being fed by the trainers).
