2. 外语
  3. The nature of light is not wholly known, but it is generally believed to be matter, as in its(1)______, it obeys the laws(2)____

The nature of light is not wholly known, but it is generally believed to be matter, as in its(1)______, it obeys the laws(2)____

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问题     The nature of light is not wholly known, but it is generally believed to be matter, as in its(1)______, it obeys the laws(2)______matter. So closely is it connected with heat and electricity that there can be (3)______ doubt of their all being(4)______ different modifications of the same substance. The effects of light(5)______ other bodies and how light is affected by them(6)______ some important principles.
    Rays of light are reflected from one surface to(7)______. It is by this reflection of light that objects are(8)______ visible. However, unless light falls directly(9) ______the eye they are invisible, and are not(10)______felt until after a certain series of operations upon the various coverings of the eye. Smooth and(11)______surfaces reflect light most powerfully, and send to the eye the images of the objects (12)______ the light proceeded before reflection. Glass would be of no use to us as a mirror, were it not first(13)______on one side, interrupting the rays in their(14)______from the glass into the air. The reason why trees, rocks and animals are not all mirrors is that their surfaces are(15)______, and rays of light reflected from such a surface are(16)______in every direction. Stand before a mirror and your image is formed and appears to be as far(17)______the glass as you are before it. Rays of light(18) ______reflected at the same(19) ______at which they fall upon a mirror, two persons can stand in (20)______ position that each can see the image of the other without seeing his own.
(9)
选项 A、upon
B、in
C、off
D、down
答案A
解析 介词辨析题。fall upon表示“落到……上”，符合文意，故[A]upon为正确答案。fall in表示“到期；集合，排队”；fall off表示“下降，脱落”；fall down表示“失败，倒塌”。
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