Answer: 2. "Thunder is good," said Mark Twain, "but it is lightning that does the work."
Step-by-step explanation: the correct answer is the second option because first, it has a comma before and after "said Mark Twain", which is correct because when we use quotation marks and we want to add information (like who said it) between two phrases, we need to put it between two commas. The other that makes this option correct is that "but" doesn't begin with a capital letter, this is correct because it is a continuation of the first quote, it shouldn't begin in a capital letter.