What are independent executive agencies?
A. Specialized agencies that regulate the economy and are not
directly controlled by the president
B. Informal advisory groups assembled by the president to serve his
or her needs
C. The major departments of the executive branch that are led by the
president's cabinet
D. Agencies with specialized functions that are controlled by the
president but exist outside of the major departments

An independent executive agency refers to a type of agency created by the US Congress using a legislative Act (statutes), so as to operate as a regulatory and service agency setting standards and overseeing the functions of the federal government.

This ultimately implies that, independent executive agencies refers to specialized agencies that regulate the economy and are not directly controlled by the president. Thus, they established to exist outside the Executive Office of the President and the federal executive departments

Some examples of independent executive agencies are Federal Communications Commission (FCC), Environmental Protection Agency (EPA), Election Assistance Commission (EAC), Consumer Financial Protection Bureau (CFPB), Central Intelligence Agency (CIA), Federal Election Commission (FEC), Federal Deposit Insurance Corporation (FDIC), etc.