input: Write a python function to reverse a given sentence using recursion.
  assert reverse_sentence("Geeks For Geeks") == "skeeG roF skeeG"
  assert reverse_sentence("Hello World") == "dlroW olleH"
  assert reverse_sentence("Python") == "nohtyP"
output: def reverse_sentence(sentence):
      if len(sentence) == 0:
          return sentence
      else:
          return reverse_sentence(sentence[1:]) + sentence[0]