The last step after replacing a defective CV boot is to ________.

The correct answer is to "burp the boot." This step is crucial after replacing a CV (constant velocity) boot because it helps to ensure that any air trapped inside the boot is released. When a new boot is installed, it may contain air pockets which can lead to improper sealing and may also interfere with the lubrication of the CV joint. By burping the boot, you allow for the proper distribution of grease, preventing dryness and ensuring smooth operation of the CV joint.

Checking fluid levels, adjusting tire pressure, and inspecting brake lines, while important maintenance tasks, are not specific steps related to the installation of a CV boot. These tasks might be performed periodically or during a comprehensive vehicle inspection but do not directly affect the newly installed CV boot's performance and integrity like burping does.