Sailing along a canal,a ship often has to go through a series of locks.Locks are like stairs for ships.They make it possible for a ship to go“upstairs”from a low body of water to a higher one or“downstairs”from a high body of water to a lower one.
A lock is simply a big water tank open at the top with watertight(不透水的)gates at both ends.When a ship going upstairs comes to a lock,the gates at one end open to let it in.Then they are closed behind the ship.Extra water is then let into the lock through pipes to raise the water level.The ship rises as a result.When it reaches the level of the water beyond the other end,the gates at that end open to let it out.Thus,lock after lock the ship raises higher and higher until at the last lock it rises to the level of the body or water outside,and it is ready to sail out of the canal.
A ship going“downstairs”will go through the same series of locks.But,of course,there is a difference in what happens at the locks.Can you tell what the difference is?
1.When talking about canals,what do we mean by a“lock”?
A.It is a tank in a ship.
B.It is something that helps keep a gate closed.
C.It is a stair with many steps.
D.It is something with walls and gates.
2.Locks are necessary when the canal __________ .
A.is very long and has many turns
B.runs through the land at different levels
C.is too shallow for large ships
D.is too narrow for ships to pass at the same time
3.Decide what the right order is for the following set of pictures explaining what happens at a lock when a ship goes through.
A.c,d,b,f,e,a B.a,e,f,b,d,c
C.e,f,d,c,b,a D.c,b,a,e,f,d
4.Which of the following is TRUE according to the pictures above?
A.The ship is going“downstairs”.B.The ship is going“upstairs”.
C.The ship could be going either“upstairs”or“downstairs”.
D.In one half of the pictures the ship is going“downstairs”in the other half it is going“upstairs”.
5.What happens at a lock when a ship is going“downstairs”instead of“upstairs”?
A.Instead of sailing forward the ship sails backward through the lock.
B.The gates are not closed at both ends:instead,they are open at one end to let water out.
C.Before the ship enters the lock,the water is lowered instead of being raised.
D.After the gates are closed,water is let out instead of being let in.
参考答案:1.D 2.B 3.A 4.B 5.D