请问一下黄皮书阅读19页的题目~

肉肉的包子脸UID: 3085318

The dark regions in the starry night sky are not pockets in the universe that are devoid of stars as had long been thought. Rather, they are dark because of interstellar dust that hides the stars behind it. Although its visual effect is so pronounced, dust is only a minor constituent of the material, extremely low in density, that lies between the stars. Dust accounts for about one percent of the total mass of interstellar matter. The rest is hydrogen and helium gas, with small amounts of other elements. The interstellar material, rather like terrestrial clouds, comes in all shapes and sizes. The average density of interstellar material in the vicinity of our Sun is 1,000 to 10,000 times less than the best terrestrial laboratory vacuum. It is only because of the enormous interstellar distances that so little material per unit of volume becomes so significant. Optical astronomy is most directly affected, for although interstellar gas is perfectly transparent, the dust is not.)  

3   It can be inferred from the passage that it is because space is so vast that
(A) little of the interstellar material in it seems substantial" E5 P" h0 q% N* m7 ^& V
(B) normal units of volume seem futile for measurements of density
(C) stars can be far enough from Earth to be obscured even by very sparsely distributed matter9 ~* ?  h* F/ D1 C, b- e
(D) interstellar gases can, for all practical purposes, be regarded as transparenta! F/ g2 |0 N4 ?
(E) optical astronomy would be of little use even if no interstellar dust existed
这个是黄皮书阅读第19页的题目，我觉得是根据倒数一二句得出答案，答案选c，请问一下a为什么不对呢，谢谢

szmanutdUID: 2727152

a文中木有体现啊
a里面说的是物质material
原文说的是单位体积什么之类的 风马牛不相及嘛

肉肉的包子脸UID: 3085318

谢谢版主大人了，原文是“so little material per unit of volume ”~

钰剑乘风UID: 3279007

请问这句话中
The average density of interstellar material in the vicinity of our Sun is 1,000 to 10,000 times less than the best terrestrial laboratory vacuum。
is 1,000 to 10,000 times less than是什么意思？