The correct answer is B. NLTK.
NLTK is a free, open-source natural language processing library for the Python programming language. It is one of the most popular NLP libraries in the world, and is used by both students and professionals for a variety of tasks, including text mining, sentiment analysis, and machine translation.
Seaborn is a Python data visualization library based on Matplotlib. It provides a high-level interface for drawing attractive and informative statistical graphics. Seaborn is not specifically designed for NLP tasks, but it can be used to visualize the results of NLP algorithms.
Scikit-learn is a Python machine learning library that provides a wide range of algorithms for classification, regression, and clustering. Scikit-learn is not specifically designed for NLP tasks, but it can be used to train and evaluate NLP models.
D is incorrect because it is not a Python library.