input: Write a python function to check the spelling of words in a sentence using a predefined dictionary.
  assert spell_check("This is my new computer") == True
  assert spell_check("Thiss is my new computter") == False
  assert spell_check("Hello world") == True
  assert spell_check("Helo wrld") == False
output: def spell_check(sentence):
      dictionary = {"this", "is", "my", "new", "computer", "hello", "world"}
      words = sentence.lower().split()
      for word in words:
          if word not in dictionary:
              return False
      return True