a generation ago的用法和样例：
- A generation ago buxom actresses were popular.
- A generation ago genetic codes were certainly unknown.
- Problems that were very appealing a generation ago may have been resolved.
- A generation ago, the symbol of economic polarization was the urban ghetto. Now it's the gated communities and other redoubts of the wealthy.
- Once before, a generation ago, world conditions had given women the chance for emancipation.
- By and large, the British working class is better off today than it was a generation ago.