Question

to people who are not familiar with computers and new technology, an online class can be confusing and frustrating. (paragraph 3)
they may not understand how to open files or access the recommended classroom materials.
a slow internet connection can make audio files stutter.
a local disruption in power can make a computer suddenly unusable for an unknown period of time.
this is clearly no replacement for a real classroom with a teacher present.

Explanation:

The original statement is about people unfamiliar with computers/technology finding online classes confusing/frustrating. The first option explains this by stating they may not know how to open files or access materials, which relates to their lack of tech familiarity. The other options (slow internet, power disruption, comparing to real classroom) are about technical issues or general comparisons, not the users' lack of tech knowledge.

Answer:

The first option: They may not understand how to open files or access the recommended classroom materials.