In the following question a statement has been given with highlighted text.…

Concept

An idiom is a fixed multi-word expression whose meaning is conventional rather than literal: it cannot be worked out by adding up the meanings of its separate words. In a replace-the-underlined-text item, the idiom you choose must carry the same sense as the highlighted words and must fit the same grammatical slot in the sentence.

Application

The highlighted words are “growing speedily”, which describe market share that keeps increasing very fast over a period of several years. The idiom “by leaps and bounds” means “very rapidly, in large increments”, and it is the standard adverbial idiom used with verbs of increase such as grow, rise, improve and progress.

Substituting it into the sentence gives: “The company’s market share has been growing by leaps and bounds in the last few years, mainly because of its strong customer base and innovative products.” The meaning of the original sentence and its grammar are both preserved.

Contrast

The remaining idioms carry senses that the sentence does not call for:

• “By fits and starts” means intermittently, in short bursts separated by pauses — it denotes irregular stop-and-start progress, not fast continuous growth.

• “By hook or crook” means by any means available, fair or unfair — it describes the manner of achieving an aim, not a rate of increase.

• “At the eleventh hour” means at the last possible moment before a deadline — it fixes a point in time, not the speed at which something changes.

Hence the highlighted words “growing speedily” are correctly replaced by the idiom “by leaps and bounds”.