Which sentence best expresses the main point? a. A main advantage of online learning is flexibility.
b. Students taking online classes are free to learn whenever they want.
c. Traditional learning forces students to gather in classrooms, but online learning does not.
d. With online learning, a student can be doing research in a foreign land and still take classes.

I can see that you haven't attached the article or paragraph.

a. A main advantage of online learning is flexibility.

Explanation:

All of the other choices presented are related to the flexibility of online learning.

For example, choice b shows how online learning gives the student the freedom to learn whatever he wants. This is an example of flexibility because the student is not restricted to learn academic subjects alone.

Choice c shows how online learning doesn't force the student to gather in classrooms. This allows the student to modify or be flexible when it comes to his location of learning.

And choice d shows how one can do multitasking through online learning. Again, this is another way of showing how you can become flexible because you can research in another country or travel abroad while not being absent from online class.

This means the rest of the choices shows how online learning is flexible.