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    Post Closed as "off-topic" by Rory Alsop, RegDwigнt
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What are the different senses of "a"?

Suppose we know that "terrorism is a serious crime".

And that "you have to report terrorism".

Can we say that

  • "you have to report a serious crime"?

I think that the bulleted statement is true. But I just took an, apparently, reputable reading comprehension test, which claimed, the point was not true despite the above.

If I'm right, which definition of "a", in that expression, makes it true?