Answer:
The sentence structure of this example is Compound-Complex.
Step-by-step explanation:
When we want to determine a sentence structure, we should analyze how many clauses it has. Clauses can be dependent or independent. Compound-Complex structure includes two or more independent clauses and at least one dependent clause. Let's see our example:
Chopin in The Story of an Hour explains to the reader; in order for anyone to live in marriage, he or she must be "Free, free, free!"
Chopin in The Story of an Hour explains to the reader - independent clause
in order for anyone to live in marriage - dependent clause
he or she must be "Free, free, free!" - independent clause
As we have 2 independent and 1 dependent clause, this sentence is a compound-complex sentence.