This is just a guess based on some quick background research I just did. I think "Bookmarking a Blog" would be the worst way to keep up with the latest blog posts.
Bookmarking a Blog: I don't think that bookmarking a blog website would send you update notifications. Therefore, I think this answer choice would be the least productive way to keep up with latest blog posts.
RSS feed subscription: RSS stands for "Really Simple Syndication" it is an easy way to distribute update notices and headlines to a large group of people. (This sounds like a good way to keep up with a blog.)
Visiting the blog every few days: This sounds tedious, but if you have the time for it I suppose this would be a good way to make sure your not missing any blog posts.
Adding the blog to an online reader: I am not quite sure what they mean by this answer choice. I am guessing that they mean adding it to a online reading list? If so, then you would be notified of any new blog posts from your blogs added to your reading list.
I hope that all made sense and that I am right in my answer! Please, let me know if I made a mistake or if I gave you the wrong answer. I would like to improve for similar questions in the future.
