Answer: The answers to your questions are
1. A. Sarah is busy today but she can go to the park with you tomorrow. - there should be a comma before but
2. A. It is such a hot humid day today. - there should be a comma before humid
3. D. Jason gets stage fright so he decided not to audition for the play. - there should be a comma before so
4. D. No running, is allowed near the pool - there shouldn't be a comma before is
5. C. Which store shall we visit first. - there should be a question mark at the end of the sentence
6. D. Babysitting my sister is more rewarding than you'd think!
Hope this helps :)