The best answer to this question is "nobody really knows". They were first brought to Great Britain from Venice (hence their English name), but they probably came to Venice from Persia. ("Persia" is a better answer than "Iran", as Venetian blinds have been around since long before Persia became known as Iran.) But we don't know that they originated there; various sources have suggested that they were first used in China, or ancient Egypt.
The last time we were asked this question – in January 2019 – the answer was Japan. If you're interested in what I had to say on that occasion, please click here. According to one source referred to in that note (but no longer available on the link I provided), "evidence for the Persian theory might be found in the name the French use for shutters or blinds, which is les persiennes." To which I would respond: it might, but it's still no more than a theory. And that means it's not a suitable subject for quiz questions.
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