Search Engine Optimization

What can happen that could change a PPC campaign from low-cost advertising to high-cost advertising?
Name a way to increase your click-through rate.
Which of three PPC tools and services researched are the best and why?
Find another PPC service, not mentioned in your resources and write a sentence containing what it is and a good feature of it.
Name an HTML tag that you should use in your site to help with SEO and why?