[单项选择]All the characteristics and abilities a person acquires and all developmental changes result from two basic, though complex, processes: learning and maturation. Since the two processes almost always interact, it is difficult to separate their effects from each other or to specify the relative contribution of each to a child’’s development. Clearly, growth in height is not learned but depends on maturation, a biological process. But improvements in motor activities such as walking, depend on maturation and learning, and the interaction between them. 　　What, then, are maturation and learning Developmental psychologists are not entirely in agreement, though there is a common core of accepted meaning. Thus all definitions of maturation stress organic processes or structural changes occurring within an individual’’s body that are relatively independent of external environmental conditions, experiences, or practice. By maturation it is meant development of the organism as a function of time
A. learning is indispensible to one’’s advancement.
B. few principles of learning are widely approved.
C. a child learns nothing unless he has desire for it.
D. learning is subject to substantial stimulation.