A Data Scientist is working on an application that performs sentiment analysis. The validation accuracy is poor, and the Data Scientist thinks that the cause may be a rich vocabulary and a low average frequency of words in the dataset.
Which tool should be used to improve the validation accuracy?

A. Amazon Comprehend syntax analysis and entity detection
B. Amazon SageMaker BlazingText cbow mode
C. Natural Language Toolkit (NLTK) stemming and stop word removal
D. Scikit-leam term frequency-inverse document frequency (TF-IDF) vectorizer