____

根据句意，写出括号内所给单词的适当形式。
____ Do you think it's good for you to keep worries to  _______ (your), boys and girls?
____ In China, it's becoming much _______ (hard) for people to pass the driving tests.
____ The government has realized the importance of the _______ (safe) of the children who take a school bus.
____ More and more teachers feel worried about some _______ (teenage) strange behaviour.

1947年夏，刘邓大军挺进大别山的消息传到陕北，***欣喜地说：“我们总算熬出头了。”这是因为（    ）

如图，三角板ABC中，∠ACB=90°，∠B=30°，AC=2$\sqrt{3}$，三角板绕直角顶点C逆时针旋转，当点A的对应点A′落在AB边的起始位置上时即停止转动，则点B转过的路径长为____ （结果保留π）．