The answer is d. Dialect is when a language belongs to a particular form or group. The other answers are in modern English but, the last answer has a more older English answer from back in the day. You know that by the use of the words "Tha's" and "an'".
D. A dialect is sort of like a style of language. A,B,C would be like a regular American person talking. The person who is talking in D would be like a Texan with a strong Texan accent/dialect.