Select the most appropriate option to substitute the underlined word segment…

Concept — An idiom is a fixed expression whose meaning cannot be worked out by adding up the literal meanings of its words. In a substitution task the replacement has to do two things at once: carry the same idiomatic sense as the underlined segment, and fit the grammar and tense of the sentence so that it still reads naturally after the swap.

Application — The underlined segment took a risk means doing something whose outcome is uncertain, in the knowledge that it may go wrong. The idiom take a leap in the dark carries exactly that sense: to act without being able to foresee the result. Its past form, took a leap in the dark, follows He just as took a risk does, so the sentence reads “He took a leap in the dark” and carries the same meaning in the same tense.

Contrast — Checking the remaining expressions against their own conventional meanings:

• took great pains — made a careful, thorough effort; this reports diligence over a task, not an outcome that cannot be foreseen.

• won laurels — earned honour or distinction for an achievement; this reports recognition received, not a chance accepted.

• took to his heels — ran away quickly; this reports flight from a situation, not exposure to possible loss.

Result — Only took a leap in the dark preserves the meaning of took a risk, so it is the appropriate substitution.