The correct answer is A. scikit-learn.
Scikit-learn is a free and open-source machine learning library for the Python programming language. It features various classification, regression and clustering algorithms including support vector machines, random forests, gradient boosting, k-means and DBSCAN, and is designed to interoperate with the Python numerical and scientific libraries NumPy and SciPy.
Seaborn is a Python data visualization library based on Matplotlib. It provides a high-level interface for drawing attractive statistical graphics.
statsmodels is a Python module that provides classes and functions for the statistical modeling of time series data. It also provides classes and functions for the statistical modeling of cross-sectional data.
None of the mentioned options are used for machine learning in Python.