The stereoselectivity of the Wittig reaction is due in part to the choice of base and steric effects, but is largely controlled by electronic effects. Stabilized ylides tend to form the E isomer of the alkene product, whereas unstabilized ylides tend to form the Z isomer as the major product. In order to stabilize an ylide, the carbanion carbon is bonded to an electron withdrawing group, such as a carbonyl. Identify each of the given structures as either a stabilized ylide or unstabilized ylide by dragging and dropping a label into the blue box underneath each structure.