Luca writes a daily blog about why people should eat healthy foods and ways to eat healthfully. What are the purposes of his blog?

to entertain and advertise

to advertise and inform

to argue and inform

to argue and entertain

Based on the given description on what Luca is posting in his blog, it is clear that the purpose of Luca's blog is (C) to argue and inform.

This can be concluded from Luca's posting on reasons why people should eat healthy foods, which means that he's trying to sway people into eating healthy food - thus an argumentative intent. He is also trying to inform people by providing ways to eat healthily.