This question was last asked (with slightly different wording) in Week 15 of the 2016–17 season (on 28 February 2017). On this occasion a different answer was given; both answers are right, but the questions setters have fallen down on opposite sides of the same hurdle.
The fact is that sliced bread was first sold in the USA in the 1920s, and in the UK in the 1930s.
On the previous occasion I wrote a summarised history of sliced bread. I also asked, "Is it just me that wishes UK question setters would indicate whether they mean a worldwide first or a UK first?"
Apparently it is.
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