Select the most appropriate option that can substitute the underlined words in…

Concept: In a phrase-substitution question the replacement must match the underlined phrase on two counts at once — its meaning and its grammatical form. The underlined phrase here is a present participle used before a noun (an "-ing" word acting as an adjective), so the substitute has to sit naturally in that same adjectival slot before the noun and carry the same sense there. So the task is: read off the sense the phrase contributes, then find the word whose dictionary sense is exactly that.

Application: The underlined phrase "coming in between" sits before the noun "months" and tells us where those four months lie — they fall in the gap between two points in time. The single participle that carries the sense "occurring or lying between two events or points in time" is intervening (from intervene, Latin inter- "between" + venire "to come" — literally "to come between"). Substituting it gives: "Within the four intervening months occurred one of the unhappiest experiences of my life." The sentence keeps its original meaning and its grammar is unchanged.

Cross-check — how the other "-ing" words differ in sense:

• skidding — sliding sideways over a surface without grip; a sense of uncontrolled motion, not of position in time.

• abating — growing less intense or dying down; a sense of decreasing degree, not of position in time.

• suggesting — putting an idea forward or hinting at it; a sense of proposal, not of position in time.

Result: the phrase "coming in between" is replaced by intervening. A useful takeaway: the Latin roots inter- ("between") and venire ("to come") combine in intervene and intervention; the related word interval comes from Latin intervallum, the space between two ramparts. All of them name something that falls between two others.