to distinguish day from night."可知，应选A。]

　　2．A sundial works by ．

　　A．tracking the movement of the stars around the sun

　　B．marking a shadow cast by the moving sun

　　C．burning candles in the sunlight

　　D．watching the stars

　　B　[细节理解题。由第三段第一句"Then it was noted that the sun cast a changing shadow as it moved across the sky."可知，应选B项。]

　　3．Which of the following was NOT used in the past to measure time?

　　A．An hourglass.　 B．A sundial.

　　C．Digital clocks. D．A pendulum.

　　C　[推理判断题。由最后一段第一句"Today，even more accurate clocks are in use，such as battery­operated quartz clocks(石英钟)，digital clocks，and clocks run by electrical tuning forks and tiny atoms."可知，数字钟是现代的产物，古代没有，故选C。]

　　4．Which of the following ways of measuring time is ordered from the least accurate to the most accurate?

　　A．Sundial，pendulum，sun.

　　B．Atomic clock，quartz clock，sundial.

　　C．Sun，pendulum，atomic clock.

　　D．Digital clock，hourglass，slow­burning candles.

　　C　[细节理解题。根据文中各种计量时间的方法出现的顺序可知，应选C。]

IV.完形填空

A very tired traveler came to the bank of a river.There was no 1 ．It was winter，and the surface of the river was covered with 2 ．It was getting dark，and he 3 to reach the other side while there was enough 4 ．On the other hand，he worried a lot，not sure whether the ice would 5 his weight.