回溯法是一种选优搜索法，按选优条件向前搜索，以达到目标。但是，当探索到某一步时，发现原先选择并不优或达不到目标，就退回一步重新选择，这种走不通就退回再走的技术，称为回溯法。
查看答案
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。
A. 对
B. 错
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
微信支付 
支付宝支付