Answer: B) sum up the subject of the chapter.
Explanation: In the given title from a chapter of "How to Live on Twenty-Four Hours a Day", we can see that the author includes the title "Controlling the mind" to give the readers a general idea of what the chapter is about, in this way, the reader know what it is most likely to be found in the chapter. Also, another function of the title is to bring the reader's attention to the content, in general is to sum up the subject of the chapter.
