有一张照片，发现其景物模糊不清，而且整个画面偏黑，其形成的原因是在拍照时，没有调节好(    )

17—18世纪，英、美、法三国资产阶级革命的共同意义有（    ）

①都推翻了外国殖民统治

②都建立了资本主义制度

③都确立了君主立宪政体

④都促进了资本主义发展

解释下列词语

①敕勒

②穹庐

看图，阅读短文，判断正误。

    Tommy is a boy. He is short and thin. He is 10 this year.

    Sally is his sister. She is 11. They go to school together.

    Tommy often gets up(起床) at 6:30 in the morning. He likes sunny days, He doesn't like rainy days.

    Tommy loves his mum. When he leaves(离开) home, he always says "Goodbye!" to her.

如图，已知△ABC中，BC＝13cm，AB＝10cm，AB边上的中线CD＝12cm，则AC的长是（　　   ）