为满足频差条件，并车时频差越小越好。
参考答案：错
解析：允许频差不能偏大也不可太小，频差在3－5S范围为好。
By the time he realizes he________into a trap, it'll be too late for him to do anything about it.[ ]
A. walks
B. walked
C. has walked
D. had walked
现代汉语
