Being safe in your everyday life needs knowledge. If you remember the following information，your life will be much safer.
● Always notice the environment around you. You shouldn't walk alone outside late at night. Make sure where the public phones are. If anything dangerous happens，you can find them easily.
●Your bag should be carried towards the front of your body instead of putting it on your back。When a bus is full of people，it is easy enough for a thief to take away the things in the bag on your back.
●If you are followed by someone you don’t know, cross the street and go to the other way, let the person understand that you know he or she is after you. Next，don't go home at once. You are safer in the street than you are alone in your home or in a lift.
●If you have to take a bus to a place far away, try to get to the stop a few minutes earlier before the bus leaves. This stops other people from studying you. On the bus，don't sit alone. Sit behind the driver or other people. Don't sleep.

北美洲和南美洲的分界线是苏伊士运河．

当显微镜的目镜为10，物镜为10时，视野范围内可以看到一行相连的8个细胞，若目镜不变，物镜换成40时，则视野中可以看到这行细胞中的  （   ）