Explanation:

- Breakthrough: A significant advance or achievement, often in the context of research or technology.

- Option 1, Discovery: The act of finding or learning something for the first time. It often leads to a new understanding.

- Correct Answer: This is synonymous with breakthrough as both indicate a major progress.

- Option 2, Disaster: A sudden event causing great damage. This is unrelated as it does not convey progress or achievement.

- Option 3, Coincidence: The occurrence of events that happen at the same time by chance. It lacks the aspect of achievement or intentional effort.

- Option 4, Accident: An unforeseen event, often causing harm. It does not imply progress or purposeful advancement.