Final answer:
The company C. Oracle, founded by former IBM employees, is a disruptive firm that instigated significant changes within the database management industry.
Step-by-step explanation:
The correct answer is C. Oracle. The company was founded by Larry Ellison, Bob Miner, and Ed Oates, all of whom were former employees of a disrupted giant, namely IBM. They left and started their own venture after being inspired by a research paper published by Edgar F. Codd on relational database systems, which IBM was slow to commercialize. Oracle Corporation is thus a prime example of a disruptive firm started by former employees of a major company that was disrupted by the subsequent innovations Oracle brought to the market. Steve Jobs of Apple and Bill Gates of Microsoft, while being disruptive entrepreneurs themselves, do not fit this scenario as they were not former employees of a disrupted giant.