One of them is "How old are you?""Well,"she answers,"I don't

One of them is "How old are you?""Well,"she answers,"I don't remember,doctor."She thinks for a minute,then says,"I remember now.When I was eighteen years old,my husband was thirty.Now my husband is sixty.I know that is twice thirty.So I am twice eighteen.Now I am thirty-six"
（）How old was her husband when she was eighteen?
A.Eighteen
B.Thirty
C.Sixty