The word accident originally meant "event", but now me

The word accident originally meant "event", but now means "unfortunate event" only. This example shows ______of meaning.
A、extension
B、narrowing
C、degradation
D、transfer
【正确答案】：B
【题目解析】：由题干得知，accident这个词原来是指“任何事件”，现在指“不幸的事件”，意义范围缩小，因此B选项为答案。见课本137页。