input: Write a function to extract the non-vowel words in a sentence. The function should return a list of words that do not contain any vowel (a, e, i, o, u) characters.
  assert extract_words("This machine learning project is challenging.")==['This', 'machine', 'learning', 'project', 'is', 'challenging.']
output: def extract_words(sentence):
      vowels = "aeiou"
      words = sentence.split()
      return [word for word in words if all(char.lower() not in vowels for char in word)]