input: from typing import List
  
  def extract_words(sentence: str, letter: str) -> List[str]:
      """Extracts all words from a given sentence that start with a specified letter.
      
      >>> extract_words('This is a sample sentence to test the program', 's')
      ['sample', 'sentence']
      >>> extract_words('Another example sentence', 'e')
      ['example']
      """
output:     words = sentence.split()
      result = [word for word in words if word.startswith(letter)]
      return result