Question

What is the main purpose of a concluding paragraph?

Answer 1

The answer to your question would be D. To restate the thesis and summarize the final point. 
Hope this helps and just ask if you need anything else! :)

Answer 2

The concluding sentence, well, concludes. So, it wraps all your main points up.

So, the main purpose of a concluding paragraph is to restate the thesis and summarize the final point