6. I think C. Tools of communication is correct option. As it's necessary to have tools of communication. The main goal of undercover role-play is to gain information. It's impossible without tools of communication.
7. I'm 100% sure that correct answer is: Trust between B. The undercover officer and the suspect is crucial for a successful undercover operation. As I've mentioned it before, undercover role-play is needed to gain useful information. To get the information, there should be trust between suspect and undercover officer.
8. As far as I remember, the answer is: When an officer watches from a stationary vantage point such as a camouflage outdoor fixture or room it is known as B. Fixed surveillance. The officer stays static during whole surveillance.
9. I'm definitely sure that this is the answer: Introduction, acceptance, buy, arrest, covering of the informant, and after actions are common steps of C. A criminal investigation. I think there's nothing to explain, as the given steps are all part of criminal investigation.