在一次爆破中，用一条96cm的导火线引爆．如果导火线燃烧的速度为0.6 cm/s，点火者在点燃导火线后，以5m/s的速度向安全区域跑去，那么他能否在爆破前跑到离爆炸点500m远的安全区？（用两种方法）

（阅读二）选择正确答案。
    Jack is a teacher of English. He is not young but he is not old. He has a round face and black hair. He is tall. There are fifty students in his class. They all like him. Now it's in the afternoon. Look some students are studying in the classroom. Jack is there too. Jack helps them to study English. He is a good teacher and he is a good friend of them all.

菠菜根的分生区细胞分裂过程中不会出现（  ）

已知函数，，有下列4个命题：
①若，则的图象自身关于直线对称；
②与的图象关于直线对称；
③若为偶函数，且，则的图象自身关于直线对称；
④若为奇函数，且，则的图象自身关于直线对称；
其中正确命题的序号为（  ）.

已知：AB⊥BC于B，CD⊥BC于C，AB=4，CD=6，BC=14，点P在BD上移动，当以P，C，D为顶点的三角形与△ABP相似时，求PB的长？