回溯法的一个显著特征是在搜索过程中动态产生问题的解空间。
查看答案
回溯法是按广度优先策略搜索解空间树。
A. 对
B. 错
I ____ Australia twice. What about you?
A. went to
B. have been to
C. had been to
D. would go to
— I’m sorry you have missed the bus. It ____ a few minutes ago.— What a pity!
A. has left
B. had left
C. was leaving
D. left
He ____ to play the piano before he was 11 years old.
A. learned
B. had learned
C. has learned
D. learns
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