Assume the Television Show Grey's Anatomy Had an Average National

Assume the television show Grey's Anatomy had an average national program rating of 18 during the 2007 season.This means that:

A) an average of 18 million households watched Grey's Anatomy.
B) 18 percent of the households watching television were tuned to Grey's Anatomy.
C) an average of 18 percent of the television households in the country were tuned to Grey's Anatomy.
D) an average of 18 million households watched Grey's Anatomy for at least five minutes.
E) 18 percent of the households in the United States watched the entire program.