What must you do when picking up a load of greasy bars?

When picking up a load of greasy bars, using the shipper's bulkhead at the rear is particularly important for securing the load effectively. The bulkhead serves as a solid barrier that helps prevent the load from sliding forward during transit, which can be crucial especially when dealing with slippery materials like greasy bars. This strategy not only enhances safety by minimizing the risk of the load shifting but also helps maintain stability while driving.

The other options, such as overlapping choke straps and double stacking for safety, may have benefits in other contexts or with different types of loads. However, they do not specifically address the unique challenges presented by greasy loads. In this case, the emphasis is on utilizing the bulkhead, which is specifically designed to keep loads in place, thus ensuring secure transport.