Which is the proper explanation of the word "fade'(L. 2, para. 3 )

A．his ability to learn would be improved
B．he would survive best
C．he would have a lot of trouble
D．the evolution of memory would stop

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