What sentence from the passage shows the author's bias? Select one:

a.
By federal law, the USPS must provide mail service to all Americans regardless of cost or location. (paragraph 3)

b.
For example, in 2012, each of the 80 billion pieces of advertising brought 21 cents in revenue, compared to 42 cents for first-class mail. (paragraph 8)

c.
In an effort to solve the postal service's problems, the government has conducted numerous studies. (paragraph 9)

d.
As you drop the letter into the mailbox, you'll not only surprise a friend or relative, you'll also help keep an American tradition alive. (paragraph 11)