input: Write a python function to summarize the given text.
  assert summarize("Natural Language Processing (NLP) is a field of artificial intelligence. It focuses on the interaction between computers and humans through natural language.", 1) == "Natural Language Processing (NLP) is a field of artificial intelligence."
  assert summarize("Artificial intelligence is the simulation of human intelligence processes by machines. Machine learning is a subset of artificial intelligence.", 1) == "Artificial intelligence is the simulation of human intelligence processes by machines."
  assert summarize("Python is a widely used high-level programming language. It is known for its ease of use and readability.", 1) == "Python is a widely used high-level programming language."
output: def summarize(text, n_sentences):
      from nltk.tokenize import sent_tokenize
  
      sentences = sent_tokenize(text)
      return ' '.join(sentences[:n_sentences])