Final answer:
On a timeline, a milestone 13 years in the future is to the right of a 4-year milestone and to the left of a 19-year milestone, indicating the relative positions of events on a timeline that progresses from left to right.
Step-by-step explanation:
On a timeline, a milestone 13 years into the future will be to the right of a milestone 4 years in the future and to the left of a milestone 19 years in the future. The correct answer is option b) Right; Left. This is because timelines are typically drawn with time increasing from left to right. Therefore, a milestone further into the future (13 years) will be positioned to the right of one that is closer to the present (4 years), and to the left of one that is even further in the future (19 years).