With its abundance of noun inflections, Icelandic is one of several Germanic languages that is compact when written but can lengthen considerably when translated into English.
(A) is compact when written but can lengthen considerably when translated into English
(B) are compact when they are written, but they can lengthen considerably when they are translated in English
(C) is compact when written but can lengthen considerably when being translated into English
(D) are compact when written but can lengthen considerably in English translation
(E) is compact when it is written but can lengthen considerably when translated in English

该题答案选D。我选了A,很多人根据one  of  that are 排除A,C,E我觉得这里that应该指代Icelandic而不是指代several Germanic languages 。而且D的后半句感觉有问题。若根据答案 one of 复数名词 + that （修饰复数)

虽然白勇语法书上讲过：

one of 复数名词 + that verb(复数)

that 从句引导的定语从句修饰复数名词，谓语动词用复数；

the(only)one of 复数名词＋that verb(单数)

that引导的定语从句修饰the(only)one,谓语动词用单数．

one of 复数名词 + that verb(复数)

that 从句引导的定语从句修饰复数名词，谓语动词用复数；

the(only)one of 复数名词＋that verb(单数)

that引导的定语从句修饰the(only)one,谓语动词用单数．

one of 复数名词 + that verb(复数)

that 从句引导的定语从句修饰复数名词，谓语动词用复数；

the(only)one of 复数名词＋that verb(单数)

that引导的定语从句修饰the(only)one,谓语动词用单数．

但是好像有些题目没有符合这个语法点。以下举例

A mixture of poems and short fiction, Jean Toomer’s Cane has been called one of the three best novels ever written by Black Americans—the others being Richard Wright, author of Native Son, and Ralph Ellison, author of Invisible Man.

1. Black Americans—the others being Richard Wright, author of Native Son, and Ralph Ellison, author of Invisible Man
     
2. Black Americans—including Native Son by Richard Wright and Invisible Man by Ralph Ellison
     
3. a Black American—including Richard Wright, author of Native Son, and Ralph Ellison, author of Invisible Man
     
4. a Black American—the others being Richard Wright, author of Native Son, and Ralph Ellison, author of Invisible Man
     
5. a Black American—the others being Richard Wright’s Native Son and Ralph Ellison’s Invisible Man

这题最后答案最后讨论是E：若根据答案one of 复数名词 + that (修饰单数)