The exercise does not say what needs to be done with a line that ends in a period, question mark comma, but does not contain the word "it". So, I assume this program runs in a universe that does not have such lines. So, I'd write (untested):

perl -nlwe 'print $1 if /\bit\b(.*[.?,])$/' text-file
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Or:

perl -nlwe '/[.?,]$/ && /\bit\b/ && print $'"'" text-file
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