input: Write a function to get the POS tag of a specific word in a sentence using NLTK.
  assert get_pos_tag("He is enjoying the warm weather", "enjoying") == 'VBG'
  assert get_pos_tag("She loves to read books", "loves") == 'VBZ'
  assert get_pos_tag("The quick brown fox jumps over the lazy dog", "fox") == 'NN'
output: def get_pos_tag(sentence, word):
      import nltk
      from nltk import word_tokenize, pos_tag
  
      nltk.download('punkt')
      nltk.download('averaged_perceptron_tagger')
  
      words = word_tokenize(sentence)
      pos_tags = pos_tag(words)
  
      for w, pos in pos_tags:
          if w == word:
              return pos