Answer: Broken line
Step-by-step explanation:
When you collect data in an experiment, you usually need a model where you can analyze the data.
One way of doing this is when in an experiment you expect a given behavior determined by a function (or data obtained by previous investigations), you can graph your obtained data over the graph of the function (or previous data), and in this way, you can see if your data fits in the model.
You usually will graph your obtained data with dots, so usually, we graph the other things with a broken line. This is because if you use a colored line and you do some kind of fitting with your data, the lines may "clash" into each other, making the graph hard to read.