请教几道语法题。。

桔色的橙

都是2000年5月的,答案都在那里了，只是想请各位高手指点为什么选？

1 The first city in the United States that put into effect major plan for the clustering of government buildings wasWashington D.C.

答案给的是B

2 Dolphins are sleek and powerful swimmers that found in all seas and, unlike porpoises, have well-defined beaklike snouts and conical teeth.

答案B。

3 A liquid taht might be a poor conductor when pure is often used to make solutions that readily transmits electricity.

答案D