input: def replace_string(sentence: str, old_word: str, new_word: str) -> str:
      """ Replace a given string with another string in a sentence.
      >>> replace_string("I love walking on the beach", "walking", "swimming")
      'I love swimming on the beach'
      >>> replace_string("Python is awesome", "Python", "C++")
      'C++ is awesome'
      """
      return sentence.replace(old_word, new_word)
output:     return sentence.replace(old_word, new_word)