We take it for granted that with memory we can remember most of things which happened in our life. But it is difficult to imagine what life would be like without memory. The meanings of thousands of everyday perceptions , the basis for the decisions we make, and the roots of our habits and skills are to be found in our past experiences, which are brought into the present by memory. Memory can be defined as the ability to keep information available for later use. It not only includes "remembering" things like arithmetic  or historical facts, but also involves any change in the way an animal typically behaves. Memory is involved when a rat gives up eating grain because he has sniffed something suspicious in the grain pile. Memory exists 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 with that of a human being. The instant access memory of a large computer may hold up to 100,000 "words"--strings of alphabetic or numerical characters--ready for instant use. An average U.S. teenager probably recognizes the meaning of about 1000,000 words of English. However, this is but a part of the total amount of information that the teenager has stored. Consider, for example, the number of faces 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 combinations of words. But while language greatly expands the number and the kind of things a person can remember, it also requires a huge memory capacity. It may well be this capacity that distinguishes humans, setting them apart from other animals. What is the major characteristic of man's memory capacity according to the author?
It can be expanded by language. It can remember all the combined words. It may keep all the information in the past. It may change what has been stored in it.