Which best explains how the structure of the office of the president fulfill the office’s role?

a the office is led by the chief of staff, who serves as a key adviser to the president.
b the office has multiple levels of staff and advisers who the president in many areas.
c the office is led by the vice president, who serves as a key adviser to the president.
d the office has a single level of staff and advisers who the president in many areas.