D). To indicate that Twain needed money in order to eat
.
Explanation:
Idioms are the most commonly employed figurative device to propose a sharp and rich language that conveys a meaning distinct from the literal meaning of the words presented. Such a device assists to present a more elaborate and spicier description offering an indirect meaning.
As per the question, the given idiom 'I..........book' functions to indicate that 'Twain required money to eat'. Twain was a realist who aimed to portray the real-life subjects with a touch of subtle elements. In this excerpt from his "I Sell a Dog", he intends to hint that he needed money for 'bread and butter'(eat). Thus, <u>option D</u> is the correct answer.