input: Write a python function to answer predefined questions.
  assert answer_question('What is the capital of China?') == 'Beijing'
  assert answer_question('What is the capital of France?') == 'I don\'t know'
  assert answer_question('What is 2+2?') == 'I don\'t know'
output: def answer_question(question):
      if question == 'What is the capital of China?':
          return 'Beijing'
      else:
          return 'I don\'t know'