以下哪类家庭对于商业健康保险的需求程度是最弱的。（ ）

A．单亲家庭

B．丁克家庭

C．单身家庭

D．扩展家庭

When Bob was eighteen, he ______ going around with a strange set of people and staying out very late.

A．took to

B．took up

C．took for

D．took on