Noun Modifiers: Plural or Singular?

Noun Modifiers: Plural or Singular?

Normally, when used as a noun modifier, it does not take the plural form. However, these are exceptions: 1) indicates variety; 2) no singular noun form exists; 3) specifies a degree or field of study; 4) specifies an office, department or division; 5) refers to a news or social issue.

** It is a sports magazine / car. (Indicates variety.)

** The Yankees were the 2009 World Series winners. (No singular form exists.)

** United States law prohibits torture. (No singular form exists.)
c.f., The state is undertaking a cost-benefit study

** The customs officer asked us questions. (No singular form exists.)

** She is studying to get a Linguistics degree. (Specifies a degree.)
c.f., She has excellent linguistic skills.

** My sister received her Creative Arts certificate. (Specifies a certificate.)
c.f., She has creative art abilities.

** Please contact the Appointments desk first. (Specifies an office.)
c.f., I have an appointment application on my computer.

** We called the benefits representative for help. (Specifies a worker in an office.)

** You will find him in the Language Arts division. (Specifies a division.)

** The gay rights issue of marriage has gone to court. (Specifies a social issue.)

** Please send me a Girl Scouts booklet. (Specifies the organization or title.)
c.f., She bought a Girl Scout uniform.

** We listened to a blues band. (Specifies the music style.)

Reference
http://www.grammar-quizzes.com/adj_nounmodifiers.html