In our city there are more and more cars and buses on the roads. Many people drive to work .First, it's good to have a car. You needn't to wait for the bus. You can go to work on time. Then ,there are many busy roads in the city . Can you drive safely? Traffic lights are very important. You must look at the traffic lights and wait for the green man. If someone is crossing the road, you must stop your car and look carefully. We must follow the rules and stay safe on the road.

15年，她们的目光聚焦着一个又一个贫困儿童，她们将阳光撒在每一个贫困儿童的心田；15年，她们为2335名贫困家庭孩子撑起走向未来的一片天空；她们用自己最真挚的爱诠释着“幼吾幼以及人之幼”的真谛。河南西峡的“代理妈妈”们的行动（    ）

已知$a,b\in R$ ，有以下命题：①若 a>b ，则ac²>bc² ；②若 ac²>bc² ，则 a>b ；③若 a>b ，则$a·2^c>b·2^c$  .则正确命题序号为____

705÷47商的最高位在____位。