( 25 )had other problems. They were made of polished
metal, which did not reflect light well. Also, metal
mirrors often cracked as they cooled after being cast.
For two hundred years opticians worked to perfect
both kinds of telescopes. Finally, in 1851, two
( 30 )Englishmen, Varnish and Mellish, found a way to
cover glass with a very thin sheet of silver. This made
it possible to build reflecting telescopes using a large
curved mirror made of silver-covered glass. These
telescopes reflected much more light than earlier
( 35 )reflectors and did not crack so easily. Today, nearly all
large optical telescopes are built on this basic design.
45. Which of the following best tells what this passage is about?(A) the design of modern telescopes
(B) how the telescope was developed
(C) the problems of early telescopes
(D) the experiments of Varnish and Mellish
(E) how lenses are made46. The passage suggests that there is usually a relationship between the size of a telescope and its(F) ability to reflect light.
(G) magnifying power.
(H) resistance to cracking.
(J) accuracy in focusing light.
(K) ability to bend light of different colors equally.47. Which of the following was a problem of early refracting telescopes?(A) They did not transmit colored light.
(B) They produced blurred images.
(C) Their glass lenses cracked frequently.
(D) They could not be used to view the stars.
(E) They were made of colored glass.