请教一道语法

翦瞳UID: 184872

01年1月
13
In geometry, an ellipse may be defined as the locus of all point__ distances from two fixed points is constant.
a. which as the sum of
b. of the sum which
c. whose sum of whose
d. whose sum that the
answer: c

28 The Unite States census (for) 1970 (showed that) the French-speaking residents of Louisiana (were) one of the country's most compact regioned linguistic (minority).
answer: d  是变成复数吗？
我觉得a 也不对啊，for 不是个时间段吗？

翦瞳UID: 184872

38 Kangaroos use (their) long and (powerful) tails (for) balance themselves (when) sitting upright or jumping.
answer:c
my answer: d when-->during

vandalUID: 2123457

13,不会，不过答案貌似不是这个

28， for 表对象，不是时间跨度

38， when可以用，但是for 作为介词后面一定不能用动词原型

lignumvitaeUID: 207532

１３，不会　同问
２８，Ｄ变成复数
３８，for后面应该是跟名词，而balance是动词原型，所以应该把for改成to

susan_0210UID: 205890

13.a，意思是在几何学中，椭圆可以定义为一个这样的轨迹，2个固定点到它上面所有点的距离和是常数。
28.恩，变复数
38.for变成to，因为后面的balance是原型。

susan_0210UID: 205890

13.空前是noun，空里应添定语——of which 或which（as a sum）of

vandalUID: 2123457

of which =which（as a sum）of  ?

翦瞳UID: 184872

13我觉得是a
which 作先导词
但仍然迷糊

hanflyUID: 195459

总觉得13怪怪的,意思大家都知道,这个结构谁能说的再清楚点

左手右指UID: 2167446

选a理由说不清楚，就是感觉，其他的感觉读不通
那位高手来解释，关注一下这个帖子

vandalUID: 2123457

In geometry, an ellipse may be defined as the locus of all point which (as the sum of distances from two fixed points) is constant.

翦瞳UID: 184872

3X vandal
It seems reasonable.

hanflyUID: 195459

qiang!
3x!

tc_zn2001UID: 187494

牛

tc_zn2001UID: 187494

好像还是C
金山词霸的定义
ellipse
The locus of points for which the sum of the distances from each point to two fixed points is equal.
椭圆到两定点的距离的和为常数的点的轨道