In the original sentence, "Somebody has stolen my book," the subject is "Somebody," the verb is "has stolen," and the object is "my book."

In the passive voice, the object becomes the subject, and the original subject becomes the agent (or is omitted). The passive construction for the given sentence is "My book has been stolen." Here, "My book" is the subject, "has been stolen" is the passive construction of "has stolen," and "by somebody" is omitted because the doer of the action is unknown or not specified.

The passive voice is used when the focus is on the action or the result rather than the doer of the action.