input: from typing import List
  
  def extract_words(words: str, letter: str) -> List[str]:
      """
      Extract all the words starting with a specific letter.
      >>> extract_words('This is a sample sentence to test the program', 's')
      ['sample', 'sentence', 'test', 'the', 'program']
      """
output:     words_list = words.split()
      result = [word for word in words_list if word.startswith(letter)]
      return result