Hi Keita Nonaka, the best answer by default will have the highest number of upvotes. We chose to automatically mark a post as resolved because we want to reduce the amount of work that the instructors have to do in their class. If an answer is not satisfactory, the owner of the post or the instructors can always mark it as unresolved. I hope that explains our product thinking.

Do you have a specific use case where you would still want a Best Answer feature?