Which one is the correct answer?

I am faced with 2 multiple choice questions and I’m not sure of the answer. If anyone knows the answer I would be appreciated to explain it to me.here are the questions:

1. It is the fact that all people are ready to try as hard as possible to become happy, ?
   I think the question tag that fits here is "don’t they?" But in another view it makes sense to ask it with "isn’t it". Now I was wondering which one would be correct.
2. The picture painted by the child was so fantastic that even great painters wondered if she …… without any help.
   A. Had painted B. Was painted
   C. have painted D. Would paint
   I think the answer is "had painted" because the first sentence is simple past. But I guess another correct option is " have painted". What is the correct answer and why?