Explain the answer please

Enlarged generally implies that something grew in 3 dimensional shape while expanded can mean both in 2 dimensional and 3 dimensional terms. If you want to get specific expanded is more correct than enlarged.

C is the correct answer. The statement is about the changing size of the road, enlarge and expand are the only responses that have to do with a change in size.

It looks like you figured it out — you crossed off options 3 and 4 (because they make no sense), answer C is the only one that contains neither 3 nor 4. Can you ask a more specific question?

I think the whole post is getting downvotes because it appears that you have the correct answer circled and don't need an explanation.

It would be helpful if you expressive what you found confusing.

The word on the tip of our tongues here is "widened." The road has been widened. Enlarged: made bigger. Yes. Expanded: made bigger. Yes. Retained: kept. No. Ruined: destroyed. No. So the answer is C, because the first and second words work

If you prefer narrow roads to wide roads, then the road has been ruined

I'd be inclined to choose 'expanded'. It has links to the verb 'to span' and that's just a word I associate with roads; they span distances.  Whereas the word 'enlarge' means to become larger. I tend to think of an enlarged photo or and enlarged tumor; generally these happen with an overall constant ratio in all directions. I could be completely wrong but it's my rationale. 

where can I get this workbook?

Well, “retain” means to keep something the same and “ruin” means to destroy something. While “enlarge” means to make something more large and “expand” means, well, pretty much the same thing in this context.

It seems to be the correct answer based on the options available, but by far the most normal way to express this is to say that the road has been widened.