The correct answer is D. the protagonist progresses from childhood to adulthood. Bildungsroman is a type of a novel which has to do with a protagonist growing up. We can see him in his childhood, we can see how he progresses through life, changes, becomes more mature and adult, which is why D is the only correct answer here. The protagonist doesn't have to be put in scary situations, or solve crimes, or face hardships - he just has to grow up. Examples would be 'Portrait of the Artist as a Young Man,' or even the Harry Potter series.