To Calculate the Herfindahl-Hirschman Index (HHI), One Must

To calculate the Herfindahl-Hirschman index (HHI) , one must:

A) sum the market shares of the four largest firms in the industry.
B) sum the market shares of all of the firms in the industry.
C) divide the market share of the largest firm by the sum of the four largest firms in the industry.
D) sum the squared market shares of all firms in the industry.