Here are the best choices to fill in the blanks for the passage:

1. **B. social media** (Nam started using a smartphone and spending too much time on social media)
2. **C. websites** (He liked joining in chit-chat and games for teens)
3. **A. notifications** (He spent a lot of time checking notifications)
4. **D. communicating** (He stopped communicating with his classmates, friends, and family members)
5. **C. helped** (he helped others)

So the complete passage would be:

Nam was a good student. But he started using a smartphone and spending too much time on (1) **social media** like Facebook and TikTok. He also liked joining in chit-chat and games (2) **websites** for teens. He spent a lot of time (3) **checking** notifications. He even neglected his schoolwork, and stopped (4) **communicating** with his classmates, friends, and family members. One day Nam saw a video clip about a boy who was addicted to games, and had no friends, so when the boy was feeling down, he (5) **helped** others. Nam realised that he also had no more friends, except his younger brother.