Context Clues

          1.Read the passage then answer the question. 

Construction on Florence's grand cathedral began in 1296. Over a hundred years later,however,the structure remained unfinished,with an enormous hole in the roof. The designers had intended to top the cathedral with the world's largest dome ,but this plan was stymied by architectural limitations. The main factor stalling progress was the fact that no one knew how to create such a massive copula without large,cumbersome support system.

What is the meaning of cupola as used in the passage?
1.dome
​2.roof
3.decoration
4.cathedral 

Dome is the answer cause in the passage it said that they are going to make a large dome and it also said that they didn't know how to make a massive cupola it means the same thing.

The other three are not right cause they don't mean the same as cupola like roof is a flat surface and they were trying to make a half sphere.