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