Answer: C. the Securities and Exchange Commission, which oversees the nation's stock markets
Step-by-step explanation:
The SEC is a line agency because they were established by an act of Congress and are given directives by Congress and the Presidency to ensure that the nation's stock market runs smoothly.
They are in the public eye more due to the policies that they implement to ensure that the market moves smoothly which further cements their designation as a line agency.
The rest are staff agencies.