- AThe board was written out by hand each morning rather than printed
- BSome of the dishes named on the board were sold out before the lunch hour ended
- CThe canteen serves the staff of one workplace and is not open to anyone else
- DThe canteen's own sales register shows that vegetable plates rise by about a fifth in those same four weeks of every year, when the new crop brings vegetable prices down, and this year's rise matched that pattern closely
Step-by-Step Solution
The rise is the one the canteen books every year in those weeks for a reason that has nothing to do with a board, and its size is the same as usual. Once the recurring seasonal movement is set against the observed rise, the whole of the rise is already explained and the board is left with nothing to account for. Handwriting, sold-out dishes and the closed clientele say nothing about why sales moved.
Answer: D) The canteen's own sales register shows that vegetable plates rise by about a fifth in those same four weeks of every year, when the new crop brings vegetable prices down, and this year's rise matched that pattern closely