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:     result = []
      for word in words.split():
          if word.startswith(letter):
              result.append(word)
      return result