What did the speaker never learn to do with the machine?

The answer is B, which indicates that the speaker never learned to operate the machine. This choice is appropriate because it reflects a fundamental skill necessary to use the machine effectively. Whether it involves understanding its controls, following operational procedures, or simply being able to engage with the machine to fulfill its intended function, not learning to operate it would prevent the speaker from ever using it.

The other options suggest skills that pertain to different aspects of engagement with the machine. Repairing implies a deeper technical knowledge and understanding of the device's mechanisms, cleaning focuses on its maintenance, and selling refers to a commercial skill unrelated to personal use. While all these actions could be relevant, they do not capture the primary necessity of learning to operate the machine itself, which is critical for any practical interaction with it.