下面文章中有五处需要添加首句。请从以下选项（A、B、C、D、E 和F）中选出符合各段意思的首句。选项中有一项是多余选项。
A. Teach children not to talk to strangers
B. Tell students to follow the school rules
C. Talk to your children about their day
D. Keep an eye on your children's Internet use
E. Teach children not to work out problems by fighting F. Tell your children a safe way to walk to school or the bus stop
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Students spend more time at school than anywhere else. At school, children need a safe and comfortable environment to help them learn. By doing the following, parents can help make sure children have a good school life.
____. Ask your children if they see anyone bullied(被欺负), if they are bullied, or if anything else makes them feel uncomfortable. Look for warning signs, such as a sudden drop in grades or a loss of friends.
____. Tell children that fighting could lead to them getting hurt, or hurting someone else. Tell them about other ways they can solve a problem, such as walking away or telling to teachers or the adult you know well.
____. Talk to your children about what they do online—what websites they visit, who they email, and who they chat with. Let them know they can talk to you if anything they see online makes them uncomfortable.
____. Teach children to follow traffic lights and rules when walking or biking. Stress that they should cross the street at crosswalks.
____. Don't go anywhere with them, or accept gifts from them when you don't know. If they see a stranger hanging around or in their school, they should tell the people that you know.
(α为参数)，在极坐标系中，C2的方程为ρ(3cosθ－4sinθ)＝6，则C1与C2的交点个数为
和
，分别垂直AB边射向棱镜，棱镜的对称轴OC为两束光的分界线，则下列说法正确的是（ ）