input: Write a function to replace a given string with another string in a sentence. The function should take three parameters: the original sentence, the old word to be replaced, and the new word to replace the old word. The function should return the new sentence with the specified replacement.
  
  def replace_word(sentence, old_word, new_word):
      return sentence.replace(old_word, new_word)
  
  assert replace_word("I love walking on the beach", "walking", "swimming")=="I love swimming on the beach"
  assert replace_word("The cat sat on the mat", "cat", "dog")=="The dog sat on the mat"
  assert replace_word("Coding is fun", "fun", "awesome")=="Coding is awesome"
  assert replace_word("Hello world", "world", "Earth")=="Hello Earth"
  assert replace_word("Python is a powerful language", "powerful", "strong")=="Python is a strong language"
output: def replace_word(sentence, old_word, new_word):
      return sentence.replace(old_word, new_word)