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.
Credibility, It increases their credibility
The Civics Disobedience was people that didt agree with what they were saying<span />
Please list out the choices, I can't help with so little information