Final answer:
The correct route for injecting a secondary IV medication alongside a primary medication is the IV piggyback. Therefore, the correct option is d.
Step-by-step explanation:
The intravenous route that uses a secondary IV medication injected alongside a primary medication is known as an IV piggyback. This technique involves hanging a smaller, secondary bag of medication alongside the primary large-volume bag. The secondary medication is administered at a controlled rate while the primary infusion continues, thereby ensuring a constant administration of both fluids. It's often used for antibiotics and other medications that need to be diluted or delivered at a slower rate than the primary fluid.