input: Write a python function to check if a number is even or odd.
  assert check_even_odd(4) == "The number is even."
  assert check_even_odd(7) == "The number is odd."
  assert check_even_odd(0) == "The number is even."
output: def check_even_odd(number):
      if number % 2 == 0:
          return "The number is even."
      else:
          return "The number is odd."