有关纬线和纬度的说法正确的是

A．所有纬线长度相等

B．纬线指示东西方向

C．两条相对应的纬线构成一个纬线圈

D．纬度是沿一个方向标注的

Questions 53 to 57 are based on the following passage:(10分)To the people of ancient Egypt,life on earth was short.Life after death,however,was eternal. Therefore they built their tombs of stone and they took their possessions with them into another world. The more important the people,the greater the tomb.The Pharaohs were the rulers of the country and when they died they became gods.Many of their tombs remain,and some have become a wonder of the world.These are the pyramids.The purpose of these stone mountains was to protect the burial chamber form the weather and from thieves who might try to steal the gold,jewels and precious possessions placed there to accompany the dead ruler into eternal life.Their shape,with four triangular sides spreading from a single point,represented the rays of the sun.their position on the west bank of the River Nile was where the sun set every day and where they believed it began its journey into the other world.All the burial grounds in ancient Egypt were on the west bank of the river.

In the last paragraph,the italicized“it”indicates

A．the sun

B．the river Nile

C．their position

D．a single point