A theme is a message or a universal lesson that a literary work expresses about a topic and that we can apply to our lives or to other literary works. Very often, this message is not directly stated in the story so we need to find it out. The sentence "Everyone has dark secrets" is a theme because it's a message that we can apply to our lives.
The options "love" and "deception", on the other hand, are topics, not life lessons. And the last option "Dr. Hyde murdered Carew" is not a theme because it can not be applied to our own lives; this sentence is more like a statement of something that happened.
