What is the structure of the following sentence?
although i have already visited africa, i would certainly like to return.

a.)simple
b.)compound
c.)compound-complex
d.)complex

The correct answer is actually letter D) complex.

Explanation:

For this sentence to be a compound-complex one, it would need to have at least three clauses, two independent ones plus one dependent one. That is not the case here, since we have only two clauses:

1. Although I have visited Africa

2. I would certainly like to return

The main clause is the second one, "I would certainly like to return (to Africa)." The first one is a dependent clause started by the subordinating conjunction "although", which introduces an idea of contrast. Since we have one independent clause - a clause that expresses a complete idea on its own - and one dependent one - a clause that needs a main clause to express a full idea -, we have a complex sentence. The best option is, therefore, letter D.