Beginner clue
Also known in the clue library as Either-Or (exactly one true).
Two questions matter more than the pattern itself: does this clue give you everything now, or only later — and does it become a mark on the board, or a note you have to keep separately?
On first read this settles nothing about which branch is true, only that the two options are different subjects. The real payoff waits until one branch is disproved.
The choice itself cannot be marked. Hold both branches in mind until the board rules one out.
Reading the clue is half the job. These are the methods that turn it into board progress.
Reading an either/or clue for the one thing it gives you immediately: the two alternatives can't be the same subject.
The moment one branch of an either/or clue is disproved, the other branch becomes true.
Writing down a fact the clue gives you that has nowhere to go on the board yet.
See this clue type on a live board, or go back and browse the rest of the library.