input: Write a python function to check if a sentence is a question based on whether it ends with a question mark.
  assert is_question("Is this a question?") == True
  assert is_question("This is a statement.") == False
  assert is_question("What time is it?") == True
  assert is_question("Please close the door.") == False
output: def is_question(sentence):
      return sentence.endswith('?')