Words are but symbols, many of which have meaning only when they

Words are but symbols, many of which have meaning only when they have acquired（）.
A、concept
B、sense
C、motivation
D、reference
【正确答案】：D
【题目解析】：Words are but symbols, many of which have meaning only when they have acquired reference. 词只是符号，许多词只有获得所指后才有意义。