同样是极地地区，在年平均气温方面，南极地区比北极地区低很多，其原因是（    ）

①纬度位置南极地区比北极地区高 ②地势南极地区比北极地区高③南极地区终年被冰雪覆盖，对阳光反射强，吸收的热量少 ④南极地区没有定居人口

根据短文内容，判断下列各句正误。

    Here's the weather report for today. It's going to be dry and windy for most of the day. Because of the wind, it's going to be cooler than usual. And the wind is going to be stronger in the evening.

    Now the report for the weekend. Our Saturday morning is going to be cloudy with little rain. And it's going to be cooler than today. In the afternoon the clouds will lift and the sun will come out. We shall have a warm evening.

    On Sunday the weather is going to change again. It's going to be fine and hot. But at noon a wind will come and it's going to be stronger in the afternoon. It's going to be a little cooler in the afternoon.

已知非零实数a，b满足$\left|2a-4\right|+\left|b+2\right|+\sqrt{\left(a-3\right)b^2}+4=2a$，则$a+b$的值为（ 　 ）．

某班同学毕业时都将自己的照片向全班其他同学各送一张表示留念，全班共送2027张照片，如果全班有x名同学，根据题意，列出方程为（      ）