问题补充：
At first driving requires a lot of concentration, but over time, it just becomes.
A. authentic
B. available
C. automatic
D. awake
答案：
A. authentic
B. available
(答案→)C. automatic
D. awake
解析：句意:一开始驾驶需要集中精力,但是一段时间后就成为无意识的行为。automatic 意思为“无意识的；不经思考的”，英语解释为done without thinking about it，这与题干中concentration（the ability to think carefully about something you are doing）相对应。authentic可靠的；真正的；available可用的；有效的；awake 醒着的;清醒的。
