Gauntlet 1 — count the threats before you trust any block. White's row is a live three, and separately white's column is a gap four that threatens FIVE at its hole — a hole that happens to sit at one end of the row three. Block the row's other end, block anywhere at all, and white simply fills the hole: five. There is exactly one square that answers both threats. Find it.
Solve the remaining tasks to finish this lesson.