The 7,000 pieces—full statues, heads and carved inscriptions—are breathtaking not only for their individual beauty, but also for 21 they represent: a road map to the origins of much of Southeast Asian culture.
答案：(A) what
what 引導名詞子句作 for 的受詞，同時兼任 represent 的受詞，意思是「它們所代表的東西（即……的路線圖）」。which 需要明確先行詞、that 不能同時當介系詞受詞又當子句內受詞、when 語意不合，皆不符合。
四個選項都是關係詞或疑問詞，你會憑語感挑一個，而 that 與 which 都很眼熟，很容易先被選走。
鑑別度高達 61。先看並列：not only for their individual beauty, but also for ______ they represent——not only ... but also ... 連的是兩個 for 後面的東西。前面那個 for 接的是名詞組 their individual beauty，所以後面這個 for 接的也必須是一個名詞性質的東西。空格後面是 they represent，一個缺受詞的子句，所以要的是一個自己帶著先行詞、整包當名詞用的關係詞——what（等於 the thing that）。填進去讀成 but also for what they represent（也因為它們所代表的東西）。
which 與 that 在限定關係子句裡可以互換，但兩個都必須有先行詞，而這一句的 for 後面直接就是空格，沒有先行詞可以接；when 是關係副詞，後面要接完整的子句，而且 for when 不成立。
what 等於 the thing that（……的東西，自己帶著先行詞）、not only A but also B（不只 A 而且 B）、a road map to（通往……的路線圖）、breathtaking（令人屏息的）、inscription（銘文、碑文）、represent（代表）。
The world's largest collection of Khmer sculpture resides at Angkor, the former royal capital of Cambodia. The 7,000 pieces—full statues, heads and carved inscriptions—are breathtaking not only for their individual beauty, but also for 21 they represent: a road map to the origins of much of Southeast Asian culture.
But the collection is not in a museum, and it is not open 22 visitors. It is held in unknown, guarded warehouses 23 only a few people can see it. These people assembled it by removing figures from the ruins of Cambodia's world-famous temples and replacing them with hollow, concrete 24. For the most part, these are hard to distinguish from the originals.
Clever art thieves? No, these "art thieves" work for the Angkor Conservancy. 25 very large pieces too heavy to move, virtually all surviving Angkorian statues, wood carvings and artifacts have been replaced with copies.