题目内容：

Scientists from Australia declared that they were able to find out how some species of birds managed to develop the ability to recognize each other’s language. Together with his partners from the School of Botany and Zoology at the Australian National University in Canberra, Professor Robert Magrath discovered that fairy-wrens (细尾鹩莺) can learn the alarm calls produced by other species of birds.

Although scientists had known that some birds could understand the alarm calls of other species and use their ability to escape danger, it was unknown how they developed this ability. There were several assumptions.

Some researchers suggested that some species of birds were able to understand the alarm calls of other species due to the fact that they were born with the ability to react (反应) to calls that are somewhat similar. There was another assumption that all birds could learn alarm calls from different species over a certain period of time.

In order to find out which assumption was closer to the truth, scientists played the sounds of alarm calls of white-browed scrubwrens (白眉丝刺莺) to fairy-wrens that live side-by-side with white-browed scrubwrens in Canberra. Alarm calls of the two species are somewhat similar. The second step was playing recordings of alarm calls of white-browed scrubwrens to fairy-wrens that live 600 km away from Canberra, in Macquarie Marshes, the region where white-browed scrubwrens don’t live. The experiment showed that fairy-wrens living in Canberra fled (逃跑) but Macquarie Marshes fairy-wrens didn’t, which, according to Magrath, had to do with learning.

Another experiment involved playing recordings of a different alarm call produced by New Holland honeyeaters. Researchers said that after hearing the calls, the fairy-wrens fled, which means that they can learn calls completely different from theirs. “They have a very sharp perception (领悟力) of other species’ calls.” said Magrath.

However, some scientists had different opinions. For example, Professor Gisela Kaplan considered that learning was not the entire reason why birds fled after hearing the alarm calls. She considered that birds’ brain features an emergency pack which includes pre-programmed (预定程序) reactions at birth. The pack may be constructed of neurons that produce a basic reflex (反射作用) when it is touched off by auditory (听觉的) reactions.

“It could be that a certain sound, like a 6 kilohertz high-pitched frequency (频率), causes that basic reflex. Where the learned part comes in is the key to correctly tell whether somebody else is simply making a high-pitch call or whether it is an alarm call,” said Kaplan. She added that her team played the same recordings to magpies (喜鹊) at various distances and discovered that their reaction was different. “It depends on whether the bird’s sound is coming from within the magpie’s territory (领地). The difference can be as small as two meters,” she said.

1.According to Paragraph 2, alarm calls produced by birds mean _____.

A. they need to flee

B. there are visitors

C. there is something to eat

D. they need help to kill their enemies

2.From the experiment in Paragraph 4, we can infer that _____.

A. birds only understand alarm calls similar to theirs

B. birds are born to understand alarm calls of other species

C. birds understand alarm calls of other species by learning

D. white-browed scrubwrens are not enemies of fairy-wrens

3.Which of the following does Kaplan agree with?

A. Magpies react violently to a 6 kilohertz high-pitched frequency.

B. Magpies learn how to tell a high-pitch call from an alarm call.

C. Birds tend to give alarm calls if danger is within two meters.

D. The location of alarm calls is important to magpies’ reactions to them.

4.What’s the main idea of the passage?

A. How do birds escape danger?

B. Birds can learn other species’ languages.

C. Birds have a sharp perception of alarm calls.

D. How do birds understand each other’s language?