HELP: 2003.10的语法第10,第34道

10.Helium is not flammable and, next to hydrogen, is ______.

(A)Known the lightest gas

(B)lightest the known gas

(C)the lightest gas known

(D)the known gas lightest

答案是C，我选的是A，能告诉我为什么选C，A为什么不对呢？？？

34.European settlers in North America moved from the Atlantic coast across 3,000 miles forests, grasslands, deserts, and mountains until they reached the Pacific Ocean.

答案是C，miles forests，我想晓得怎么改，谢谢了！！！！周六就考了！希望能尽快得到答复～～～～～～～～～～～

10。如果要用A的格式的话，应该是known as teh lightest gas

34.   改成3,000 miles of forrests

谢谢啊～但是，34题，不可以用3000 MILES 来修饰FORESTS吗？ 不是名词可以修饰名词的吗？

经典解释!

不可以用3000 miles forrest，光修饰forrest也是错的，只能说3000 miles of forrest，或者3000-mile forrest