Here are the corrections for the underlined parts:

1. She meets (A) an (B) old friend at (C) a (D) dinner party last weekend.

   • Correction: She met an old friend at a dinner party last weekend.

2. There are (A) a big traffic jam on (B) the road to (C) the (D) downtown.

   • Correction: There is a big traffic jam on the road to downtown.

3. The (A) teachers had (B) a meeting at (C) 6 o'clock on the afternoon.

   • Correction: The teachers had a meeting at 6 o'clock in the afternoon.

4. We have a (A) smoke detector on (B) the ceiling in (C) each classrooms (D).

   • Correction: We have a smoke detector on the ceiling in each classroom.

5. She don't know (A) whether she left (B) her book at (C) school or on (D) the bus.

   • Correction: She doesn't know whether she left her book at school or on the bus.

6. Schools in (A) America are (B) closed at (C) Thanksgiving Day and the (D) day after.

   • Correction: Schools in America are closed on Thanksgiving Day and the day after.

7. We can find out (A) about schools in (B) the past by (C) looking to (D) evidence.

   • Correction: We can find out about schools in the past by looking at evidence.

8. I heard a heavy (A) footstep on (B) the stairs when I close (C) my book at (D) 9.30 p.m.

   • Correction: I heard heavy footsteps on the stairs when I closed my book at 9.30 p.m.

9. The (A) students love camping (B) on (C) the mountain on summer holidays (D).

   • Correction: The students love camping in the mountains on summer holidays.

10. In (A) some cities, people don't feel safety (B) when going (C) out alone at (D) night.

• Correction: In some cities, people don't feel safe when going out alone at night.