What compound-complex sentence can be formed from the underlined section of the passage?
Have you ever thought about traveling to another country? Pick a place that interests you, and where your native language is not spoken. Once you have picked a place, you can research language-learning options. You can use online programs or find a class. You could learn and practice with a friend, and then take a dream vacation. Learning a language can be difficult. It is one of the the most useful hobbies. I’ve tried it.

-Learning a language can be a difficult and useful hobby; I’ve tried it.
-Learning a language can be difficult; it is one of the most useful hobbies I’ve tried.
-Learning a language can be difficult, it is one of the most useful hobbies I’ve tried.
-Learning a language can be difficult, yet it is one of the most useful hobbies that I’ve tried.

Learning a language can be difficult, yet it is one of  the most useful hobbies that I've tried.

Explanation:

A compound-complex sentence is a sentence which consists of two (or even more) independent clauses and at least one dependent clause. These clauses are joined by a conjunction. In this case, the independent clauses are: 1) "Learning a language can be difficult" and 2) "it is one of the most useful hobbies". These clauses are joined by a conjunction "yet", and a dependent clause "that I've tried" is added, which makes a compound-complex sentence.

i highly recommend james madison. the work is simple and if you stick to it you can graduate quickly. the work is simple and the teachers are very interactive. the flow of the school work is all on your time so it's not really a dead line. go on their website and look at pricing and enrollment plans. i know when i signed up i got a discount. you pay a certain amount of money every month. it's kind of expensive but i did it in 6 days tops with just my senior year left : )