1. The correct answer is dialects.
A dialect is a substandard form of a language - this means that it is a type of a language spoken in one area of a country, and it is usually not completely grammatically correct. If you take a look at the excerpt above, you can see that it is definitely not formal - using expressions such as 'woulda,' 'being brung,' etc. is rather colloquial.
2. The correct answer is credible.
When Mark Twain used colloquialisms and dialects in his novel, he wanted to portray these people as they were. He wanted his readers to believe him, to think that there are really people like that, and to be able to imagine the spirit of the time perfectly.
3. The correct answer is realist.
Mark Twain was a realist writer - the authors during the era of Realism (19th and part of 20th century) wanted to portray real people, emotions, events. They didn't want to embellish their literature, but rather to write about actual people, believable people, credible people. Mark Twain was no different.
