An explanation makes clear how things work or why things happen．It opens with a general statement and then lists points which explain how or why．
● Which is more salty，water from a tap or water in the sea？
● Where do rivers run to？
The sea is salty because salt is washed into the sea from the land．
First，rain washes salt from the ground，and this salt dissolves（溶解）in the rainwater before running into the rivers．When the rivers flow into the sea they carry the salt with them．
Every year millions of tonnes（吨）of salt are washed into the sea，and when water evaporates（蒸发）from the sea，the salt is left behind．This means that the sea contains more and more salt as the years go by．
The Red Sea and the Dead Sea are more salty than the oceans．This is because they have many rivers flowing into them．Also，they are inland seas and not very big，so the salt builds up．The extra salt in the water makes it very easy to swim in these seas．
Answer the following questions．
1．Does salt dissolve in water？
2．What carries the salt to the sea？
3．How much salt is washed into the sea each year？
4．Which seas are easy to swim in？
5．Is the Red Sea more salty than the Atlantic Ocean？
6．Will the sea become more salty as time goes by？Why？
7．What else do you think rivers carry to the sea besides salt？
8．What other things dissolve in water？
9．Whatdo you think it would be like to swim in the Dead Sea？
10．Write true or false after these sentences．
When water evaporates from the sea，salt is left behind．
The oceans are more salty than the Red Sea or the Dead Sea．
Salt is carried into the sea by rivers that flow into the sea．
（Keys：1．Yes，salt dissolves in water．2．Rivers carry the salt to the sea．3．Millions of tonnes of salt are washed into the sea each year．4．The Red Sea and the Dead Sea are easy to swim in．5．Yes，the Red Sea is more salty than the Atlantic Ocean．6．Yes，because more salt will be washed into the ocean．7．Answers may vary—mud，earth，plants，fish，bones，rubbish and so on．8．Answers may vary—sugar，honey，jelly cubes，instant coffee powder and so on．9．Own answer．10．true；false；true）
Glory from Comprehension
