28) D. although Internet services are rather easy to use, you will find considerable difficulties if you are not familiar with it.

(29) A. know English is one of the most important aspects that help you use the Internet. Learning may take a few hours, a few days, or some weeks, but it takes years to learn a language.

(30) C. fluently, of course, when you know some English, your English should be good enough to understand

(31) A. use it on the Internet.

So, the complete passage would look like this with the chosen answers:

(28) D. although Internet services are rather easy to use, you will find considerable difficulties if you are not familiar with it. (29) A. know English is one of the most important aspects that help you use the Internet. Learning may take a few hours, a few days, or some weeks, but it takes years to learn a language. (30) C. fluently, of course, when you know some English, your English should be good enough to understand (31) A. use it on the Internet.