Which of the following tools is primarily focused on natural language processing?

BERT, which stands for Bidirectional Encoder Representations from Transformers, is a tool specifically designed for natural language processing (NLP). It is a transformer-based model that has transformed how we approach tasks such as sentiment analysis, question answering, and language translation, among others. BERT is highly effective because it considers the context of words in a sentence bidirectionally, allowing it to understand the meaning of a phrase based on surrounding words rather than in isolation.

The other tools mentioned have different primary focuses. Scikit-learn is primarily a machine learning library that provides tools for data mining and data analysis, designed for more general machine learning tasks rather than specifically for NLP. TensorFlow is a comprehensive open-source platform for machine learning that can be used for various types of tasks, including but not limited to NLP, computer vision, and more various deep learning applications. OpenCV is primarily utilized for computer vision tasks, such as image processing and real-time computer vision applications, making it less relevant to natural language processing.

Thus, BERT stands out as the tool primarily focused on NLP, given its design and effectiveness in processing and understanding human language.