Sarah has decided to write a speech about her favorite animals, dogs. She narrows her topic to training dogs and decides the purpose of their speech will be "How to train your dog." Sarah brainstorms a list of questions about her topic.

1. Who are some famous dog trainers?
2. Are there different styles of training?
3. What are the most important things to teach your dog?
4. Why should you train your dog?
5. How do you teach your dog to sit?
6. How to teach your dog to stay?
7. How to teach your dog to lay down?
8. How to teach your dog walk on a leash?
9. How to teach your dog to come?
10. What do you need to start training?

After eliminating the unnecessary questions, Sarah knows she has to combine some topics if she only wants to have 5 main points. Which questions should Sarah combine?
a. 5 and 7
b. 6 and 10
c. 4 and 5
d. 9 and 10

Please select the best answer from the choices provided.