which of the following topics is too broad for a 10-minute speech

Modes of transportation is too broad of a topic for a 10-minute speech.

Imagine all of the different types of transportation you can think of. I can think of cars, airplanes, boats, bicycles, etc... There are so many different types of transportation that it would be impossible to talk about all or even a decent amount of them within a 10-minute speech. All of the other topics are much more specific, making it easier to focus on just a few main points.

Modes of transportation

Explanation:

The first three topics are very specific, in fact, they are pieces of larger topics, so they are more likely to be covered in a few points. The modes of transportation topic, on the other hand, is too broad and unspecific. To define each mode of transportation, their use, importance, interactions with one another and advantages and disadvantages (which are some of the most basic points you will probably have to talk about) would be covered in at least a 30-minute speech.

the answer to "what does the narrator realize by the end of the story" is b.