小刚同学要用A4纸（长约30cm，宽约21cm）绘制校园操场（有周长400米的标准跑道）示意图，他选取的最合适的比例尺是（  ）

从基因型为Aa的绿色植物某器官中获取组织，显微观察如下图。下列对该图所示细胞的叙述正确的是(　　)。

   When it rains, do your shoes get wet? Of course they do! But you can buy these pretty red and white “Umbrella for Shoes”. They keep the rain off wet.
   Who sweeps the floor at your home? Do you do it yourself? Perhaps your mother does it. Well, now you just need a cat. Get a cat and buy these four “Dusters (抹布)for Cats ”.
   You talk too long on the phone, don’t you? Most teenagers do! Save time – buy the “Telephone Dumb–bell (哑铃)”! It weighs five kilos. Then your calls will be less than five minutes.
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