What might be left on full-bearing vines during pruning?

The correct answer highlights the importance of maintaining the right balance of vine growth during the pruning process. For full-bearing vines, it's essential to leave some structures intact to ensure ongoing productivity in subsequent seasons. Bearing units, renewal spurs, and replacement spurs are left behind deliberately, as they serve different purposes in the health and yield of the grapevines.

Bearing units are the parts of the vine that produce fruit, thus they are crucial for the continual harvest. Renewal spurs are short sections of stems that can generate new shoots for the future, essentially "renewing" the vine's capacity to produce. Replacement spurs help to maintain the vine's structure and ensure that it has adequate young wood for future growth. By leaving these components, the vineyard manager enhances the vine's longevity and productivity, ensuring that there will be a balance of old and new growth, which is vital for sustainable grape production.

In contrast, other options would compromise the vine's ability to produce in future seasons. Leaving only old wood or new growth might not provide the necessary balance, and removing everything entirely would hinder future grape yields.