Select the most appropriate option to substitute the underlined segment in the given sentence. The food intolerance industry has grown dramatically in the previous decade, chiefly because of a boost in Coeliac and Crohn’s disease cases, as well as increasing awareness among health-conscious clients.

Correct — C. The underlined segment is "chiefly because of a boost", so the replacement has to supply a degree word, a causal link and a noun of increase.

"owing primarily to" does the first two: "primarily" carries the force of "chiefly", and "owing to" is the standard formal link for a cause.

"a rise" is the noun English takes for cases of a disease going up. A "boost" is something deliberately given, so it sits oddly beside illness.

The segment then reads: "...grown dramatically in the previous decade, owing primarily to a rise in Coeliac and Crohn's disease cases..."

Why the others are wrong

• (a)
  pretty much entirely because of a boil-down — "boil-down" means a reduction to essentials — the wrong direction for an industry that grew. "Pretty much entirely" also overstates "chiefly" and is too informal for the sentence.
• (b)
  contextually because of a spark — "contextually" is not a degree word and cannot replace "chiefly". A "spark" is a sudden trigger, not the sustained increase a decade of growth needs.
• (d)
  casually due to a growth — "casually" means in a relaxed, offhand way. It is the near-twin of "causally" and the real trap here — the slot needs a word for degree, not for manner.

Segment-substitution items test collocation — which words habitually travel together — as often as they test grammar.

The frame here is [degree adverb] + [causal link] + [noun of change], and a correct option has to fill all three slots without shifting the meaning.

"Rise", "increase" and "growth" describe something going up by itself. "Boost", "spark" and "boil-down" all imply an agent or an event acting on it, which is why they misfit a count of disease cases.

Key facts

• "Owing to" introduces a cause and matches the formal register of this sentence.
• "Casually" means in a relaxed manner and is not a synonym of "causally".
• "Boost" implies something applied deliberately, so it collocates badly with disease cases.
• A "boil-down" is a reduction, the opposite of the increase the sentence describes.

Common traps

• Choosing on register alone and picking the longest, most formal-sounding option.
• Reading "casually" as "causally" because the sentence is about a cause.

No directly related past PYQ was found.