Answer:
The best answer to the question: Which quotation correctly uses ellipsis to shorten Twain´s words, would be: the second one "and there is no reason why I shouldn´t".
Explanation:
The reason for this being the correct answer comes from understanding the purpose of an ellipsis, or ellipses. Ellipses are punctuation marks, just like comas, or periods, that have the specific purpose of marking portions of a written sentence, paragraph, passage, or an entire text, that are not really needed information, but rather added, and which if removed from the text will not affect the overall comprehension of the meaning of the text. In this case, Twain saying "and there is no reason why I shouldn´t" in regards to how long he expects to live, is added information to the main passage that if removed from it will not affect the overall understanding of his meaning.
