Learning is an essential process for living things to acquiring necessary skills and behav

iours. Scientists have already found that there is a critical period for learning in man and animals. Once the right time for learning a skill or a certain behaviour has passed, this skill or behaviour can never be properly learned.

Thorpe of Cambridge University found that the chaffinch has to learn most of its songs, and that this learning has to occur during the early weeks of the bird's life and also during the first spring. If the bird is handreared and isolated from other birds from the time of hatching, it sings only very simple songs and it never learns the song of its species correctly.

That we speak our own language perfectly and the languages we learn later imperfectly also depends on learning this skill at the right time. The brain develops in such a way that it is ready to learn to speak between the ages of about ten months and ten years. Languages learned later are not spoken perfectly. The ability to speak a language is a mixed motor and sensory skill. It is necessary to hear all the sounds, the subtle differences between similar but not identical sounds, the rhythm and lilt of the language. One has also to work tongue, throat, and lips, to control breathing. All this has to be managed at one and the same time. From some time after birth until the age of six or seven, normal children can learn all this perfectly, and without much difficulty they can learn two or even three languages at the same time, without muddling them up. But later, most of us cannot acquire this skill. We may learn to write and read the new language perfectly; but to acquire the right inflexion and the accent and the ability to speak so that no one can detect that the language is not our mother-tongue hardly ever occurs.

But those of us who still want to learn foreign languages after these early milestones have been passed need not worry; for though we may not learn to speak a new language like the natives, we know from thousands of examples that we can go on learning languages beyond the age of eighty. There are so many activities adding to the simple word "learning" that although some of the processes become less efficient with ageing of the brain, our actual experience of learning helps us in learning new material.

According to the study by Thorpe, a chaffinch reared in isolation after its birth ______.

A．never sings

B．cannot learn songs from other species of birds

C．never sings as well as other chaffinches

D．sings the same song all the time