Exercise 1: The Full Key Sequence Into a Rescue Shell — Possible Solution
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1. At the GRUB menu, press 'e' on the default (highlighted) entry.
2. Locate the line beginning with "linux" (the kernel boot command).
3. Move the cursor to the end of that line.
4. Type a space, then append: systemd.unit=rescue.target
5. Press Ctrl+X (or F10) to boot with this edit applied.
6. The system boots into a minimal rescue shell with root access.

Explanation:

This follows the chapter's own numbered walkthrough exactly, step for
step. Pressing 'e' opens the live, temporary editor for that one
entry -- nothing here touches disk, matching the chapter's own
explanation that edits made this way are gone on the very next
reboot. Appending systemd.unit=rescue.target to the existing linux
line (rather than replacing the whole line) is important -- the
existing root=UUID=... and other parameters are still needed to
actually locate and mount the correct root filesystem; only the extra
parameter is being added on top. Ctrl+X commits the edit and boots
immediately with it in effect, landing in the rescue shell described
in the chapter, ready for the actual fix (resetting a password,
correcting fstab) before a normal reboot.

WHY THIS WORKS AS AN ANSWER
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This reproduces the chapter's own six-step sequence precisely,
including the detail that the parameter is appended to the existing
line rather than replacing it, and explains why each step matters
rather than just listing keystrokes.