you should think over it ---- you make your own decision

在你做决定之前,你应该仔细思考. 既: 三思而后行
所以 A 正确
until 1.直到...时,到...为止
Will this fish keep until tomorrow?
这鱼能搁到明天吗?
2.(用于否定句)在...之前,直到...(才)
She didn't go to bed until eleven o'clock.
她直到十一点才上床睡觉.