Answer:
a. add a reference line whose value follows a reference parameter
Step-by-step explanation:
To dynamically change a reference line using parameter action, you first create a reference parameter. Next, add a parameter action for it. Finally, "add a reference line whose value follows a reference parameter."
This is because to dynamically change a reference line using parameter action, one needs to do the following:
1. Attribute the reference line with a parameter
2. Utilize a parameter action to make the parameter interactive.
3. As your users interact with the view, the reference lines automatically update to deliver more context to the data.