input: Write a python function to tokenize a given sentence using nltk library.
  assert tokenize_sentence("This is a sample sentence for tokenizing.") == ['This', 'is', 'a', 'sample', 'sentence', 'for', 'tokenizing', '.']
  assert tokenize_sentence("Hello, world!") == ['Hello', ',', 'world', '!']
  assert tokenize_sentence("NLTK is a powerful tool for text processing.") == ['NLTK', 'is', 'a', 'powerful', 'tool', 'for', 'text', 'processing', '.']
output: import nltk
  nltk.download('punkt')
  
  def tokenize_sentence(sentence):
      from nltk.tokenize import word_tokenize
      return word_tokenize(sentence)