I will try to give the reader of this article some idea of the real history of Gothic architecture, not just of Venice, but of universal Gothic. One of the most interesting parts of our study will be to find out how far Venetian architecture went in achieving the perfect type of Gothic, and how far it fell short of it. The author's purpose is to do what?

This question is missing the options. I've found the complete question online. Since the passage is the same, I will omit it:

The author's purpose is to do what?

1. explain the importance of Gothic architecture.

2. show how Venetian architecture is different from Gothic architecture.

3. describe Venetian architecture.

4. show the nature of Gothic architecture.

The author's purpose is to:

4. show the nature of Gothic architecture.

Explanation:

The author states his purpose very clearly right at the beginning of the passage:

"I will try to give the reader of this article some idea of the real history of Gothic architecture, not just of Venice, but of universal Gothic."

The author will discuss the nature of Gothic architecture - what this style of architecture consists of. He makes it clear that he will not focus only on the Gothic of Venice. He will talk about it universally. He will indeed show how far Venetian architecture went in terms of this style, but this is not the main purpose of the study. Having that in mind, the best option is number 4:

4. show the nature of Gothic architecture.

the rhyme scheme is abab cdcd efef gg.