Each object you can manipulate or place on the graph has its own unique features as well as some features that are shared with other graph objects. A common feature is that each of these items, when required, will be represented on the palette. As long as a particular palette symbol remains in color, you may drag additional instances of that object onto the graph. Note that sometimes you will be given more instances of a particular object than you are required to place on the graph, so just because the palette remains in color does not mean you must place additional items on the graph.