什么是顺铣？什么是逆铣？数控机床的顺铣和逆铣各有什么特点？

若x2=9，则x=______；若 3 y =-2，则y=______．

如图所示，在光滑绝缘水平面上有两个分别带异种电荷的小球A和B，它们均在水平向右的匀强电场中向右做匀加速运动，且始终保持相对静止，设小球A的电荷量为QA，小球B的电荷量为QB，则下列判断正确的是（   ） A．小球A带正电，小球B带负电，且QA＞QB B．小球A带正电，小球B带负电，且QA＜QB C．小球A带负电，小球B带正电，且QA＞QB D．小球A带负电，小球B带正电，且QA＜QB

对于双索面斜拉桥主梁，预应力控制在恒载+活载作用下，构件不出现拉应力范围。( )

When you are curious about something, and want to know more about it, you can use the way of asking questions. Asking questions is the first step to make discoveries and find interesting answers. The steps below can guide you during the research.

Step 1 On a note card or piece of paper, write down the subject that you are interested in. Just get the main idea down. For example, you might write:

Discover more about dinosaurs.

Step 2 Next, stop and think for a moment about what you already know about your subject. List what you already know like the sentences below:

1. Dinosaurs lived long before human beings appeared.

2. Dinosaurs lived on the earth for more than 150 million years.

3. Some dinosaurs fed on plants, some on meat.

Step 3 What can you do with what you want to learn? By asking questions. On your paper, start writing down questions about the dinosaurs as you think of them:

1. What’s the best weather for dinosaurs to live in?

2. How many kinds of dinosaurs are there?

3. Have dinosaurs really disappeared?

Step 4 Armed with your list of questions, you can now go to the nearest library or computer to begin your research. As you learn more about your subject, you’ll probably discover some new questions.

For example, you might discover that dinosaurs disappeared about 65 million years ago. Why? What happened? Asking new questions can help you research your subject more widely.

The next time you find something interesting to research, take time to organize your thinking by asking good questions. And remember—learning more always bring more questions.

小题1:When you do some research, you should take the following steps:                .

①list what you want to know      ②choose a research subject

③list what you already know      ④discover new problems

A．①④③②

B．②③①④

C．③②④①

D．④③①②小题2:What does the underlined sentence “Armed with your list of questions” mean?

A．Putting your list of questions under your arm.

B．Discussing your questions with your classmates.

C．Writing down your list of questions.

D．Taking your list of questions with you.小题3:According to the passage, which of the following is TRUE?

A．You can find all the answers online.

B．Learn more, and you’ll have no questions.

C．During the research, you may keep finding new questions.

D．Asking questions is the only way for research.小题4:. The best title for this passage is              .

A．Discovering Dinosaurs

B．Asking Good Questions

C．Finding Subjects

D．Having Interesting Answers

______的任务是诊断和改正程序中的错误。