There are many different kinds of parrots in the world. They can not only(不但)live in the tree, but they can also(而且)live on the mountain. Some parrots are quite big. Some are very small. Many people like them, because they often have beautiful colours, and because they can “talk”.

    Do you know why parrots can talk? But most birds cannot. Perhaps, parrots can “talk” because they have big, thick tongues. But some other birds that cannot talk have big, thick tongues, too. So we don't know why parrots can talk.

有四位同学分别用一个主题概括了1368﹣1840年的明清（鸦片战争前）时期总的历史特点。对此概括最准确的是（    ）