It is difficult to imagine what life would be like without memory. The meanings of thousands of everyday perceptions, the bases【B1】the decisions we make, and the roots of our habits and skills are to be【B2】in our past experiences, which are brought into the present【B3】memory. Memory can be defined as the capacity to keep【B4】available for later use. It includes not only 'remembering' thing like arithmetic or historical facts, but also any change in the way an animal typically behaves. Memory is【B5】when a rat gives up eating grain because he has sniffed something suspicious in the grain pile. Memory is also involved when a six year old child learns to swing a baseball bat. Memory【B6】not only in humans and animals but also in some physical objects and machines. Computers, for example, contain devices for storing data for later use. It is interesting to compare the memory storage capacity of a computer【B7】that of a human being. The instant access memory of a large computer may hold up to 100 000 'words' ready for【B8】use. An average American teenager probably recognizes the meanings of about 100 000 words of English. However, this is but a fraction of the total【B9】of information which the teenager has stored. Consider, for example, the number of facts and places that the teenager can recognize on sight. The use of words is the basis of the advanced problem solving intelligence of human beings. A large part of a person's memory is in terms of words and【B10】of words. 【B1】