Final answer:
The key consideration in selecting a human resource information system (HRIS) in this case is scalability.
Step-by-step explanation:
In this case, the key consideration in selecting a human resource information system (HRIS) would be scalability. Scalability refers to the system's ability to handle growth and changing needs. With a financial services company that expects significant growth in staff over the next 5 years, it is important to choose an HRIS that can accommodate this expansion without compromising overall performance.
While cost is also an important factor, it does not directly address the specific needs of accommodating 30 percent growth each year. Usability and extensibility may be relevant considerations in general, but they are not as critical as scalability in this particular scenario.