In a parallel circuit, adding more light bulbs does not change the brightness of the existing bulbs. Each bulb has its own path to the battery, receiving the full 15 volts.
If you are looking for an answer key for Activity C of the Circuits Gizmo (often found on ExploreLearning), here is a helpful review of what the activity covers, the concepts you need to understand, and a guide to help you find the correct answers yourself. circuits gizmo answer key activity c