People appear to be born to compute. The numerical skills of children develop so early that it is easy to imagine an internal clock of mathematical maturity guiding their growth. Not long after learning to walk and talk, they can set the table with impressive accuracy--one plate, one knife, one spoon, one fork. Soon they are capable of noting that they have placed five knives, spoons, and forks on the table and, a bit later, that this amounts to fifteen pieces of silverware. Having thus mastered addition, they move on to subtraction, It seems almost reasonable to expect that if a child were secluded (使...隐居) on a desert island at birth and returned seven years later, he or she could enter a second-grade mathematics class without any serious problems of intellectual adjustment.
Of course, the truth is not so simple. This century, the work of cognitive(认知的) psychologists had illuminated the subtle forms o？ daily learning on which intellectual progress depends. Children were observed as they slowly grasped concepts that adults take for granted, as they refused, for instance, to concede that quantity is unchanged as water pours from a short stout glass into a tall thin one. Psychologists have demonstrated that young children, asked to count the pencils in a pile, readily report the number of blue or red pencils, but must be coaxed (哄) into finding the total. Such studies have suggested that the basics of mathematics are mastered gradually, and with effort. They have also suggested that the very concept of abstract numbers is itself far from innate.
What does the passage mainly discuss？

A. Trends in teaching mathematics to children.
B. The use of mathematics in child psychology.
C. The development of mathematical ability in children.
D. The fundamental concepts of mathematics that children must learn.