I read this question without reading the answer and chose the correct answer using a process of elimination.
I reached the correct answer, but I can't be sure if the author of this question had the same thought process.
I got down to either B or C, and then eliminated C because I felt like a road map is generally discussed as features to be released where as a story map decomposes features into related user stories that can be delivered at different times.
I feel like B is always true, where C is only sometimes true.
You could potentially develop a product increment for feature 2 before you finish all the product increments needed to complete feature 1.
The story map is at a more detailed level than a road map and doesn't necessarily roll up exactly to the road map.