When having an adjective, as opposed to a verb, "to be" does require something to denote it's there.
And, the adjective would not agree with the gender and number of the subject.
I. E. חתולה זה דבר רע
Or חתולה זה רע
I'm not entirely sure I understand why חתולה רעה means "bad cat" whilst החתולה רעה would mean "The cat is bad" and not "The bad cat"
I'm not sure exactly how to explain it, but to say "the bad cat" it would be "החתולה הרעה".
"החתולה (היא) רעה" effectively becomes "the cat (she) is bad", if you eliminate the words in brackets, if that makes sense.
Why is "The cat is bad." wrong? I thought the solution should be a sentence since there is a full stop.
I had the same problem. I thought it might be רעה but it sounded like there was a full stop after the resh