Step 1: Understanding the Concept.
“Unto This Last” is a well-known essay collection on political economy that deeply influenced Mahatma Gandhi's thinking, including his idea of Sarvodaya.
Step 2: Check the options.
Boris Yeltsin was a Russian President, not a writer of this book, so option A is wrong. Pushkin was a Russian poet unrelated to this work, so option B is wrong. Ruskin Bond is a modern Indian author of fiction, easily confused by name with the real author, so option C is a distractor and wrong.
Step 3: Final Answer.
“Unto This Last” was written by John Ruskin, the English art critic and social thinker, so option D is correct.