Shea rubs a silk cloth on a glass rod to create new charges in the materials. After doing this, he notices that the materials are attracted toward each other. The new charges in the two objects are shown as question marks (?) in the diagram. Which of the following best describes the new charges of the particles in each material? glass rod: positive / silk cloth: neutral glass rod: positive / silk cloth: negative glass rod: negative / silk cloth: neutral glass rod: positive / silk cloth: positive