Yes very true but here motto was to ask which keywords are meant file handles and answer would be STDIN, STDOUT, STDERR

Then please write STDIN, STDOUT, STDERR. I thought you did mean a, b and c.

And a, b, c are also valid file handles:

$ perl -wE 'use strict; open a, "<", "TODO"; say <a>'
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It is also slightly annoying to have several correct answers within a poll; the question which of several correct answers is more correct doesn't make sense, if you start thinking about it.

Thanks for the quiz anyway.