While working with MS-DOS which key is used to get the p[revious command used:

In MS-DOS, the key used to get the previous command used is Option A: F3. Pressing F3 on the keyboard while working in the MS-DOS prompt retrieves the last command entered, allowing you to quickly repeat it without typing it again.

Option B, "F1," typically displays help information in MS-DOS applications.
Option C, "F6," and Option D, "F9," do not have specific functionalities related to retrieving previous commands in MS-DOS.

Therefore, the correct answer is Option A: F3.