A digital memory card containing photographs of Brad Pitt, Angelina Jolie, and their children (was/were) stolen.
subject: "a digital memory card containing photographs of Brad Pitt, Angelina Jolie, and their children"
participial phrase: "containing photographs of Brad Pitt, Angelina Jolie, and their children"
prepositional phrase: "of Brad Pitt, Angelina Jolie, and their children"
verb: "was/were stolen"
The simple subject, "memory […]