Suppose you have a blogging website wherein you share your thoughts on the latest developments in technology. The length of each post varies and you wish to have a dynamic scrolling, that is$,$ the scroll bar will adjust according to the size of the post once you publish a post. Note that the behaviour of the scroll bar will change at run$-$time depending upon how much the user has scrolled or written on the blog. Which of the following design patterns would you use for this purpose?