Update README.md

README.md

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 ## Introduction
 The **Cermat Czech MultiChoice** dataset was collected from assignments official CERMAT website. The dataset was collected from three tiers of assignments:  6 year, 9 year primary school test and final high school tests (so-called maturita).
 The assignments were semi-manually extracted from official PDFs available at [CERMAT's website](https://maturita.cermat.cz/menu/testy-a-zadani-z-predchozich-obdobi/matematika/testy-a-zadani-matematika).
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+**Collection Date Range**: years 2016-2023
 
 ## Licensing and Credits
 The majority of collection work was done by our student co-worker Jan Kapsa.