The problem is 18 when airplanes fly at higher altitudes, where the difference between the inside and outside pressure increases, causing added stress.
答案：(D) intensified
intensify 是「加劇、增強」，本句指飛機飛得愈高、內外壓力差愈大，問題就愈嚴重；disguised（被掩飾）、understood（被理解）、confronted（面對，被動須用 be confronted with）語意都不合。
答對率 32%。
你認得形容詞 intense（強烈的）與名詞 intensity（強度），卻很少把動詞 intensify（加劇）記起來，再加上這裡用的是被動 is intensified，字形一變就認不出來。
when airplanes fly at higher altitudes, where the difference between the inside and outside pressure increases, causing added stress——increases 與 added stress 兩個訊息都指向「更嚴重」。
intense（強烈的）／intensity（強度）／intensify（加劇）／intensive（密集的，intensive care 加護病房）。
confronted 的問題在句型：要說 be confronted with a problem（主詞是人），本句主詞是 the problem，位置剛好顛倒。
the problem is intensified（問題加劇）、intensify one's efforts（加緊努力）、intensive care（加護病房）、at high altitudes（在高空）。
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.