To eliminate any irregularities at the pulse transition corners, you measure the pulse's rise time when it is at what percentage of full voltage?

The correct choice involves measuring the rise time of a pulse at the 10% to 90% of its full voltage levels because this range effectively captures the most critical section of the pulse transition. The rise time, defined as the time taken for the pulse to change from 10% to 90% of its maximum voltage, is significant because it excludes the time spent in the slow rising or falling parts of the waveform that may not accurately reflect the pulse's transition characteristics.

By focusing on the 10% to 90% range, you ensure that you are measuring the pulse's performance during the steepest part of its rise, thereby eliminating any anomalies present at the lower and upper voltage thresholds. This method provides a more reliable and repeatable measurement that is widely accepted in electronics and signal integrity analysis.

The other options, while still defining certain points in the pulse shape, do not adequately cover the essential transition area needed for a consistent rise time measurement. Specifically, measuring at only one fixed point or narrower ranges would not accurately represent the rapid changes occurring in the transition region.