I guess formal and informal refer to two types of essay - you can write a formal essay where you avoid conversational language and such and where you need to be very professional, or you can write informally where you don't have to think about such things, it is very casual.
Answer:
1. The city of Sacramento is the capital of California.
2. Jennifer and Peter will travel to russia to work in an orphanage.
3. The Jackson Elementary School band will perform "Yankee Doodle."
4. My friend Sally and I are reading the novel The Phantom Tollbooth.
5. The train will stop in Atlanta, Montgomery, and Jacksonville.
6. Nicole likes Pepsi, but Veronica and Brandon prefer Coke.
7. The faces of four presidents are carved on Mt. Rushmore.
8. Are you going to go to Celeste's party on Saturday?
9. The new school year will begin in August or September.
10. The American Women's League meeting will be held on Tuesday.
11. We celebrate Valentine's Day in February, not in October.
12. Sarah planned a Christmas party at Lakeshore Park this December.
The correct sentence is:
Every day there are more comments, and they are hard to ignore. The antecedent of the pronoun "they" is "comments".