语法200101/13

13. In geometry, an ellipse may be defined as the locus of all points -------distances from two fixed points is constant.

(A) which as the sum of(B) of the sum which(C) the sum of whose(D) whose sum that the

 答案C。我看着4个选项都不对，请多批评。

大全的解释还是不清楚，all points the sum of whose distances from two fixed points is constant 这部分看着糊涂：

－all pints 和the sum中间是否有省略that/which were?

－简化句子the sum is constant, 如果正确，whose distances from two fixed points不就缺谓语了吗？

还是请高人分析一下结构

我是这样理解的，还请大家指正：

the sum of whose distances(主语)
            from two fixed points（定语从句省略which is）
            is（谓语） constant.

横线后面是一个完整句，

A和B 姑且不谈句意，which后面+不完整句，所以错；

D可看出that可以充当引导定语从句的引导词或是同位语从句的标志词，如是前者则后面应该跟不完整句，如是后者则应后面是个名词性短语，而实际跟的是完整句，所以错。

只能选C了！

首先，你题没抄全

13. In geometry, an ellipse may be defined as the locus of all points, -------distances from two fixed points is constant.

省略了一个逗号，有了这个逗号以后，the sum of ... 做 the locus of all points的同位语.