in the pack ice of the Antarctic，say it is so effective that it produces a meal for the whales three out of every four times they use it.

Dr.Robert Pitman，a marine scientist at the National Oceanic and Atmospheric Administration in California，said，"The killer whales were very good at knowing in advance if they were going to be able to wash a seal off a piece of ice and they were always successful in getting the seal into the water.Sometimes the seal was washed off but managed to flee.However，it was not very often."

Dr.Pitman and his colleague Dr.John Durban helped BBC capture the wave­washing behaviour on camera.By swimming in formation(队列) towards the ice from as far away as 150 feet，the whales created a bow wave in front of their bodies.When they reached the block of ice where the seal was hiding，they dove under the ice，kicking their tails in a powerful stroke(击) to create a large wave that washed over the ice and knocked the seal into the water where they could grab it and drown it.

Research has shown that there are at least four types of killer whales living in the Antarctic，all of which have different colour patterns and hunting behaviour，and eat different things.The largest killer whale hunts minke whales in open water while the ice killer whales mainly hunt seals.A third type of killer whale mainly preys on penguins and the fourth dives deep to hunt fish.

5．According to Paragraph 1，killer whales hunt a seal on a piece of ice by .

A．pushing the ice onto the ground

B．knocking hard on the ice together

C．creating large waves to wash it off the ice

D．following it all the time until it swims in the sea

答案　C

解析　细节理解题。根据第一段最后一句"The killer whales work together as a group to create large waves that wash seals off the ice."可知这种鲸鱼通过制造大浪把海豹从冰上冲刷下来，然后捕食它们。

6．It is implied in the passage that .

A．killer whales often stay hungry

B．killer whales usually hunt alone

C．competition among killer whales is very fierce

D．killer whales are very good at hunting seals at sea

答案　D