Cette pomme est bonne. - Oui, c'est bon.

Question

I got this question:
Cette pomme est bonne. - Oui, c'est _______.

I answered bon because I knew to use the masculine, but my question is why it's c'est in this case. I've read the relevant pages (https://progress.lawlessfrench.com/my-languages/french/review/4671/2123437 and https://progress.lawlessfrench.com/my-languages/french/view/3006) and my interpretation is that this would fall under 2b of https://progress.lawlessfrench.com/my-languages/french/view/4671: 
il est/elle est  for statements and opinions related to specific things.

Answer

To add to this, the English translation provided by Kwiziq was:
This apple is good. Yes, it is good.
Had it said "This apple is good. Yes, they are good," then « Ce sont bon » would have made sense to me (versus « elle est bonne »).

Answer

My issue with Kwiziq is that when I ask a question, I get back "We don't speak French" - not what I would have expected.

Answer

Hi Max - you may have had that response from someone on our email customer support as that is for technical and billing-related support and not all email support staff are qualified French teachers.

However, language questions posted here on the Q&A will be answered both by our qualified language experts as well as other members of our learner community, some of whom have an impressive level of French.

Hope that explains that response!