The word "silly" used to mean “happy”, but now means “foolish”.

The word "silly" used to mean “happy”, but now means “foolish”. This example shows（） of meaning.
A、extension
B、narrowing
C、degradation
D、transfer
【正确答案】：C
【题目解析】：词义从褒义变成贬义，意义上发生了降格。