A new analysis of satellite-based data has given precisely the rate 21 which the country is losing size as it pushes northward against the Himalayas.
答案：(D) at
the rate at which 是固定結構：原句為 the country is losing size at a certain rate，介系詞 at 隨關係代名詞一起前移，成為 the rate at which…；by／in／of 都不是 rate 慣用的介系詞。
看到 the rate 後面接著 which，多數人第一個反應是「關係代名詞前面該擺哪個介系詞」，然後開始比 by、in、of 哪一個順。順序反了。這一格真正要問的是前面那個名詞 rate 平常配哪個介系詞——先知道 at a rate（以某種速度、以某種比率），關代前面該擺什麼才有得判斷。記憶裡沒有 at 這一格，怎麼推都是猜。
先把句子還原成兩句：A new analysis has given the rate.（一項新的分析給出了那個速度。）加上 The country is losing size at that rate.（這個國家正以那個速度縮小。）第二句的 at 本來就跟在句尾，改寫成關係子句時，at 跟著關係代名詞一起搬到前面，就成了 the rate at which…。這裡有一個很穩的驗算法：把 at which 拆回句尾唸一遍，唸得通就選對了。at 這一格屬於「配數值刻度」的那一組，一起記最省力：at a rate of two centimeters a year（以每年兩公分的速度）、at the age of 18（在十八歲時）。一句記完：My classmates skim the news at a rate of three headlines a minute, but few of them finish a whole report.（我同學一分鐘掃過三則標題，卻很少有人把一整篇報導讀完。）〔情境取材自 108 指考作文題：青年對各類新聞的關注度〕
by which（藉由…的方法）：rate 是刻度不是方法，還原成 losing size by that rate 唸不通。in which（在…之中）：後面要接空間、範圍或時期（the year in which…），速度不是可以待在裡面的東西。of which（…的）：會讀成「那個速度的國家」，語意錯位。三個都不是 rate 慣用的介系詞——關鍵不在關代怎麼配，在名詞自己帶的那個字。同義記一組：at a rate of ＝ at a speed of。
at a rate of（以…的速度、比率）、at a speed of（以…的時速）、at the age of（在…歲時）、at a price of（以…的價格）、the rate at which（…的速度）、shrink by（縮小…幅度）、a sign of（…的徵兆）、a trivial finding（微不足道的發現）。
India is shrinking. A new analysis of satellite-based data has given precisely the rate 21 which the country is losing size as it pushes northward against the Himalayas. According to the analysis, the 22 between India's southern and northern tips shrinks by 2 cm every year. As India's size decreases, the thickness of the Himalayas increases. 23 the shrinking continues, India will disappear in 200 million years. There would only be a vast mountain range along the southern coast of China.
The Indian plate's 24 movement is not new. However, this cannot be treated as a trivial finding in science. A movement of 25 a few millimeters (mm) of the earth's crust is a sign of possible earthquakes. Such dangers are now obvious in India, where the movement of the plate continues.