I came across this question when doing some JLPT N2 practice.
I think that all three options are correct syntactically. All three are periods of time, so I thought I should choose the semantically best answer - b. This is because the other two options are not as worth talking about. I mean, "consecutive holidays" sounds more like a topic to chat about/discuss than just "May" or "a week". b also makes sense because during consecutive holidays, people do tend to travel a lot, so it would be natural for a town to have a lot of visitors during that time.
However, the correct answer is c and I don't see why. My book says this about the use of にわたって:
So I should put a long period of time (幅が大きい) before にわたって. However, the correct answer is just a period of one week. And speaking of 五月の連休, I can only think of Golden Week, so my answer also is a period of one week.
Why is the correct answer c and why are the other answers wrong?