C. The blogger's videos help teenagers because they... 1. explain difficult topics in an interesting way. 2. are usually very long and serious. 3. include quizzes at the end of each video. 4. talk only about sports events.

Ответ: 1. explain difficult topics in an interesting way.

1. В тексте сказано: "There is a popular blogger who makes short videos explaining what's happening in the world. He does it in a fun way and sometimes invites real reporters or scientists. It helps us understand difficult topics without getting bored."
2. Из этого следует, что видео блогера объясняют сложные темы в интересной форме.

Ответ: 1. explain difficult topics in an interesting way.