When subjected to repeated pressurization high in the sky, the four corners on a square window may 19 .
答案：(C) spell disaster
【句型】spell disaster 字詞搭配「意味著災難/導致嚴重後果」，表示方形窗戶的四個角可能會「導致災難」（破裂）；cause conflict（引起衝突）、rebuild strength（重建力量）、endure shock（承受衝擊，語意方向不合）都不合。
spell 你只認得「拼字」，所以 spell disaster 看起來像「拼出災難」，完全對不上。spell 當動詞另有一個常考語意：招致、意味著（不好的結果），後面固定接負面的名詞——spell disaster（後果不堪設想）、spell trouble（要出事了）、spell the end of（宣告……的終結）。
先看整段鋪的因果：sharp corners are natural weak spots where stress concentrates（尖角是應力集中的天然弱點）→ the difference between the inside and outside pressure increases, causing added stress（內外壓力差變大，壓力增加）→ When subjected to repeated pressurization high in the sky, the four corners on a square window may ___。前面鋪的全是「危險累積」，而文章一開頭就講過 three planes mysteriously broke apart in midair（三架飛機在空中離奇解體）。空格要填的正是這條危險線的終點。
cause conflict（引起衝突）用在人與人或立場之間，不是物理結構；rebuild strength（重建強度）方向完全相反，尖角是弱點不會愈撐愈強；endure shock（承受衝擊）同樣是相反的——四個角如果撐得住，飛機就不會解體了。這一題答對率只有 41%，多半就是把 endure shock 讀成了正確方向。
spell disaster／trouble（意味著災難／麻煩）、spell the end of sth（宣告……的終結）、be subjected to（遭受、承受）、weak spot（弱點）、break apart（解體）、stress concentrates（應力集中）。
Airline passengers may have noticed that all plane windows have rounded edges, instead of the hard corners commonly found in our house. The round windows are indeed pleasant to the eye, but they actually were designed for reasons 16 aesthetics.
In the early days of aviation, plane windows 17 square in shape. Then as commercial air travel became popular in the 1950s and airplanes began flying higher and faster, three planes mysteriously broke apart in midair. The cause? Square windows. Scientists found that sharp corners are natural weak spots where stress concentrates. The problem is 18 when airplanes fly at higher altitudes, where the difference between the inside and outside pressure increases, causing added stress. When subjected to repeated pressurization high in the sky, the four corners on a square window may 19 .
Curved windows, on the other hand, distribute stress around more evenly, reducing the likelihood of cracks or breaks. Circular shapes are also stronger and resist deformation, and therefore can 20 extreme differences in pressure inside and outside of an aircraft. Thus, round windows are a major safety innovation that keeps planes from disintegrating mid-flight. They are also used on ships and spacecraft for their greater structural integrity.