The tone of the passage can best be described as ______.

A．forgetfulness is a response to learning
B．the memory storage system is an exactly balanced input-output system
C．memory is a compensation for forgetting
D．the capacity of a memory storage system is limited because forgetting occurs

A．interpret the function of forgetting
B．illustrate the process of adapting
C．explain the performance of memory
D．emphasize the importance of learning