Recall the Application About Unwanted Commercial E-Mail, or Spam, to Answer

Recall the Application about unwanted commercial e-mail, or spam, to answer the following question(s) .
-According to the Application, the amount of e-mail spam would significantly decrease if

A) the cost of sending spam exceeded its profitability.
B) states passed laws making spam illegal.
C) e-mail filters were developed to separate spam from legitimate e-mail.
D) more people responded to spam e-mails.