A：How old are you?
你多少岁?
B：That's a secret.
那是秘密。
注释：
secret(秘密)有下列重要词组：
in secret偷偷摸摸地
例：Laura's parents don't like her boyfriend, so she meets him in secret.
(劳拉的父母不喜欢她的男友，所以她偷偷和他见面。)