Well, it depends on the exercise. If it's a listening exercise, if it's a man speaking, you need to put it exactly as he said it, not as you would put it, as a woman. If it's a regular translation, it should accept both versions. Maybe you made another mistake you didn't notice?
Thank you for such a quick reply, it was a standard written sentence and to fill in the missing word, it was not spoken. The missing word itself was "speak". I just typed it into google translate and apparently what I chose was "talking". So the correct was מדבר instead of מדבות. With the ending of "ת" I was thinking along of the feminine version. Once again thank you for the reply!