Why should you not set your transmit frequency to be exactly at the edge of an amateur band or sub-band?
To allow for calibration error in the transmitter frequency display
So that modulation sidebands do not extend beyond the band edge
To allow for transmitter frequency drift
All these choices are correct✓Correct answer
Explanation
Your emission, not just your dial reading, has to stay inside the band, and dial calibration error, drift and the width of the modulation sidebands can all push energy over the edge. Because each of the three reasons is real, the combined answer is correct.