A. In Windows 98 and later, you can drag the taskbar one row at a time (if it isn't locked) to fill half the screen or hide it entirely. However, I recently encountered a problem where the taskbar wouldn't reduce to the default setting of one line (it either appeared as two lines or none, but not one).
I discovered that the problem was that I had a toolbar set to start directly underneath another toolbar, which I was able to confirm by unlocking the taskbar (right-click the taskbar and clear the checkmark next to "Lock the Taskbar"). As this figure shows, two separate group start lines were set to start one directly above the other. To resolve the problem, I dragged the lower group start line up to the other group start line and resized the taskbar to appear on one line.