下列各函数中，最小值为2的是（   ）

    马达加斯加水冲玛瑙出产于贝奇布卡河口处一段5千米左右的河段中（如左图），玛瑙被河里的软泥包裹着，亿万年受到绵绵密密的冲刷，形成了光滑、圆润的表皮。玛瑙的寻采，主要由当地土著居民使用简单工具徒手完成，当地政府严禁外国人采挖，也不允许使用机械采挖。右图为马哈赞加气温与降水资料图。

阅读下列短文，从每题所给的四个选项（A、B、C和D）中选出最佳选项。

    Four seasons make a year. They a re spring, summer, autumn and winter. 

    Spring is a beautiful season. It's from March to May. In spring, trees turn green and flowers come out. Everything looks new.

    Summer is a happy season. It's from June to August. The weather is hot, so people usually wear cool clothes, go swimming and eat ice cream.

    Autumn is a colourful season. It is from September to November. In autumn, leaves on trees turn yellow. Sometimes they are yellow and red. The colours are beautiful.

    Winter is the last season. It's from December to February. In China, the weather is not the same in winter. In Beijing, it's very cold. It often snows. People often play with snow and go skating in rivers and lakes. Skating is their favorite sport in winter. But in Haihan, it's not very cold. It's very warm. People there can go swimming in the sea.