Circular shapes are also stronger and resist deformation, and therefore can 20 extreme differences in pressure inside and outside of an aircraft.
答案：(A) tolerate
語意「圓形形狀能夠『承受』極端的壓力差異」，tolerate（承受/容忍）符合；improve（改善）、justify（證明合理）、obtain（獲得）都不合。
tolerate 你背的多半是「容忍（別人的行為）」，帶著人際互動的味道，所以用在「圓形能 tolerate 壓力差」會覺得怪怪的。tolerate 也可以用在物體上，指承受得住、耐得住（高溫、壓力、惡劣環境），這是科普文章裡很常見的用法。
同一句的前半已經給了同方向的鋪陳：Circular shapes are also stronger and resist deformation（圓形也比較堅固、能抵抗變形）。and therefore 把前後綁成因果——既然堅固、能抗變形，接下來自然是「承受得住」極端的壓力差。resist 和 tolerate 在這裡是同一個方向的兩個字。
improve（改善）：圓窗不會讓壓力差變小，只是撐得住；justify（證明……正當）的受詞通常是說法、決定或行為；obtain（獲得）方向不對，壓力差不是要去取得的東西。
tolerate（承受、耐得住；容忍）、tolerance（耐受度、容忍）、be tolerant of（容忍……）、resist deformation（抵抗變形）、withstand pressure（承受壓力）、structural integrity（結構完整性）。
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.