Opening Move: Find a Naked Single

This challenge begins with a cell, not with a race to finish the grid. Your task is to collect the restrictions around one location and show that only one digit survives. The rest of the puzzle is available if you would like to continue afterward.

Before writing, name the digits already present in the target cell's row. Then inspect its column and its outlined box. Combine the exclusions rather than treating any one unit as the whole test. A digit that is absent from the row may still be blocked by the column.

Use a separate candidate list if the cell is too small for notes. Cross off a digit only when you can point to the placed copy that blocks it. If your list is empty, recheck the coordinates and the original clues. If more than one option remains, check the third unit again.

After the first placement, update its peers and look for one immediate consequence. You may find a second single or simply improve a candidate list. Either outcome is useful practice in keeping a deduction separate from the next question.

5 . . | . . . | . . .
1 7 . | 4 . . | 8 3 .
9 8 . | 6 1 . | . . .
------+-------+------
7 . . | . 2 6 | . 5 8
. 6 . | . 8 . | . . 7
8 . 5 | 9 7 3 | 6 1 2
------+-------+------
. . 7 | . . 1 | 5 8 3
. 5 . | 7 6 9 | . . 4
. . . | . . . | . . .

Your task

Find every legal candidate for r3c9. Which digit must go there, and which units exclude the alternatives?

5 2 4 | 3 9 8 | 7 6 1
1 7 6 | 4 5 2 | 8 3 9
9 8 3 | 6 1 7 | 2 4 5
------+-------+------
7 3 9 | 1 2 6 | 4 5 8
2 6 1 | 5 8 4 | 3 9 7
8 4 5 | 9 7 3 | 6 1 2
------+-------+------
6 9 7 | 2 4 1 | 5 8 3
3 5 8 | 7 6 9 | 1 2 4
4 1 2 | 8 3 5 | 9 7 6