Foresight means the ability to predict or prepare for the future, which is conceptually similar to farsightedness (literally the ability to see far, figuratively the ability to plan ahead).
The relationship is one of conceptual similarity rather than physical similarity.
Option (A) — long : lengthy — is a pair of near-synonyms in a purely descriptive sense, not conceptual.
Option (B) — further : farther — are also near-synonyms related to distance but not abstract qualities.
Option (C) — short : dwarf — is a physical size comparison but not conceptual.
Option (D) — thinker : visionary — parallels the conceptual similarity: a visionary is a forward-thinking kind of thinker, much like farsightedness is a forward-looking aspect of foresight.
Thus, (D) is the correct analogy.