单数。指的是一整个家庭做主语，这里是一个整体，所以做主语时，谓语动词用单数。a family of mice的中文翻译是老鼠家族，mice是mouse（老鼠）的复数形式。
a family of mice的例句
The cellar was dark and forbidding; moreover, I knew a family of mice had nested there.
这个地窖阴森可怕；而且我知道那儿有一窝老鼠。
The dark room had a threatening earance; furthermore, I knew a family of mice had nested there.
那间黑屋子外观很吓人；而且，我还知道里面住了一窝老鼠。
family的用法
1.family作“家庭”讲的用法
Almost every family in the country owns a television.
这个国家几乎家家都有一台电视机。
My family is large.
我的家是个大家庭。
2.family作“家庭成员”讲的用法
His family are all waiting for him.
他的一家人都在等他。
My family go to the park.
我家人去公园。