如图所示，电源电动势为E，内阻为r，当滑动变阻器的滑动端向右移动时，则（   ）

一个球的质量为m,用绳系着放置在倾角为θ的光滑斜面上,细绳处于竖直方向上,如图所示,则斜面对球的支持力为(       )

下图是2012年世界小姐选美大赛中，各国佳丽汇聚一堂，她们不仅种族、肤色不同，眼球颜色也不一样。聪明的你一定知道，决定眼球颜色的结构是（  ）

细胞分裂后，新细胞的染色体形态与数目和原细胞相比有什么变化（   ）

This is my school. There are many trees and flowers in it. The teaching building is big and tall. There is a big playground in our school. After 4:30 in the afternoon, many students come to the playground to play football and some students play table tennis in the table tennis room.
There are 1,200 students in 25 classes in our school. The students all like to study. The teachers in our school are very good. They help the students to study and the students like them, too.