Đáp án đúng là A

Script:

(Mai is having a video call with her penfriend in Singapore-Chris)

Chris: Hi, Mai. How’s everything?

Mai: Not bad. We still have lessons online every day. But this morning, when we were studying the power went off suddenly.

Chris: Really? Modern technology sometimes causes us problems.

Mai: Yeah... By the way, do you like studying online?

Chris: Well, yes. It's convenient and comfortable. You don't have to get up early and get dressed for class.

Mai: But it's difficult to concentrate. And I still want to go to class. I want real interaction with my teachers and friends.

Chris: Yeah... and learning online all day long causes us headaches and sore eyes.

Mai: Sure. And do you think that modern technology is greatly changing our lifestyle?

Chris: Yes, technology changes the ways we communicate with others.

Mai: And it improves our friendship because it's easy to keep in touch with people living far away.

Chris: Certainly.

Mai: Technology is also changing how we live and work.

She found it difficult ___________ (teach) 50 students online.