问题 单项选择题

对如下二叉树,进行后序遍历的结果为【 】。

A.ABCDEF

B.DBEAFC

C.ABDECF

D.DEBFCA

答案

参考答案:D

解析:后序遍历可以描述为:若二叉树为 空,则空操作;否则:①后序遍历左子树;②后序遍历右 子树;③访问根结点。对于后序遍历,第一个访问的结点一定是最左下的结点,最后一个访问的结点一定是根结点,如果知道这个小技巧,可以迅速确定本题的答案为选项D)。

阅读理解

阅读理解。

                                                       Obama still smokes in secret

     US President Barack Obama may have just made life more difficult for cigarette makers, but he still

smokes every now and then in secret.

     Obama, who has publicly struggled to quit smoking, said he still hasn't completely kicked the habit

even after signing a law this week that will likely set tough new rules for the tobacco industry.

      "As a former smoker I constantly struggle with it. Have I fallen off the wagon sometimes? Yes. Am

I a daily smoker, a constant smoker? No," Obama said at a news conference.

     "I don't do it in front of my kids, I don't do it in front of my family. I would say that I am 95 percent

cured, but there are times where I mess up," he said.

     The new law gives the US Food and Drug Administration the power to strictly limit the making and

marketing of tobacco products.

      At a White House signing ceremony Monday, Obama said that he was among the nearly 90 percent

of smokers who took up the habit before their 18th birthday.

      "Once you go down this path it's something you continually struggle with, which is exactly why the

law we signed is so important because what we don't want is kids going down that path in the first place,"

he said at the news conference.

     Nearly 20 percent of Americans smoke and tobacco use kills about 440,000 people a year in the United

States due to cancer, heart disease, and other serious diseases.

1. According to the passage, Obama _______.

A. was cured of a disease

B. had an accident

C. made Americans' life difficult

D. signed a law this week

2. What does the underlined sentence mean in the third paragraph?

A. Have I dropped from the wagon?

B. Have I stopped smoking completely?

C. Do I still smoke sometimes?

D. Do I still smoke as much as before?

3. Which of the follow is NOT TRUE?

A. Nearly 90 percent of the population of America smoke.

B. Nearly 90 percent of the smokers of America began to smoke before they turned 18.

C. Nearly 1/5 of Americans smoke.

D. Smoking kills about 440,000 people a year in the USA.

4. The new law first looks at _______ health.

A. adults'

B. middle-aged people's

C. women's

D. children's

单项选择题