TASK DEFINITION: You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For consistency, answers should be in all lower cased letters.
PROBLEM: Category: WORLD "P"s 
Clue: Malay or Sinai

SOLUTION: peninsula

PROBLEM: Category: THE 1930s 
Clue: On September 18, 1934 the Soviet Union joined this international organization

SOLUTION: league of nations

PROBLEM: Category: UP IN THE SKY! 
Clue: Over 90 nations have agreed to a total ban on CFCs by the year 2000 to protect this atmospheric layer

SOLUTION:
ozone layer