问题 单项选择题

已知二叉树后序遍历序列是dabec,中序遍历序列是debac,它的前序遍历序列是

A.acbed

B.decab

C.deabc

D.cedba

答案

参考答案:D

解析: 依据后序遍历序列可确定根结点为c;再依据中序遍历序列可知其左子树由deba构成,右子树为空;又由左子树的后序遍历序列可知其根结点为e,由中序遍历序列可知其左子树为d,右子树由ba构成,如下图所示。求得该二叉树的前序遍历序列为选项D) 。
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多项选择题
阅读理解

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

There's an old saying, “You can put more salt in the soup,but once it's in there,you can't get it out.”__1__ And your child can help!Here's an exciting experiment for your child to try:

Start by helping your child to mix salt into the water in the mixing bowl and stirring until it is fully dissolved溶解).

___2__ Make sure that you don't let any of the salty water into it.

___3__ Then take a small rock,and place it right on top of the center of the plastic wrap,so that all of the plastic leans slightly toward the middle of the bowl where the cup is.

Put the whole setup in full,hot sun,and wait. Within an hour, you should see water droplets begin to form on the underside of the plastic. __4___

Wait, and then take the plastic off. A good amount of water should be in the small cup.

__5__ Guess what? No salt!The water vaporized蒸发)in the heat of the sun,and then returned to its liquid state. Salt doesn't do that一it stayed behind. You really can take the salt out of salt water!

As it happens,this is an excellent lesson in the way matter can change states.

A.Fresh water is scarcer than ever.

B.Invite your child to taste with you.

C.Water can go from liquid to gas and to liquid again.

D.Cover the bowl with plastic wrap and seal the edges.E.Then place a cup or a smaller bowl into the center of the bowl.

F.They'll flow and drip into the center of the bowl,and into the cup.

G..Today, scientists are busy exploring ways to take the salt out of salt water in large quantities.