Uncountable (mass) nouns refer to substances, concepts,or general terms for classes of items. The following words are uncountablenouns: oxygen (substance), education (concept),equipment (general term).
Do not use an article with an uncountable noun ifyou are referring to the noun in a general sense.
Marie and Pierre Curie discovered the radioactivity in1898.
Marie and Pierre Curie discovered radioactivity in 1898.
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