If there is an answer for the constructed response, can I mark A instead of zero?

No. If there is any typed response at all within a constructed response, you should not use the Non-Score code of "A." The score may be a zero, but any text at all that is typed for a constructed response, such as a little as one keystroke, should not receive a Non-Score code. The Non-Score code selection in ScorePoint is available beneath the number scores feature on the Score Responses page.

Screenshot of the Non Score Codes