以下关于关系模式关键字的说法中不正确的是 (55) 。A) 关键字不能取空值 B)

南方丘陵山区农业资源综合开发的主要做法是（）

①发展鱼塘—台田模式②优势资源的系列开发③发展立体农业④小流域综合治理

A．①②

B．②③

C．③④

D．①④

发动机电子点火系的点火能量，由（）来控制。

A.点火线圈初级通电时间

B.点火线圈的次级电流

C.火花塞间隙

D.点火线圈的次级电压

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。

We all know that money can’t buy happiness. No matter how much we earn, or how nice our clothing or cars or toys are, none of it will make us happier. __小题1:_____ and the sad thing is that it could take us decades of pursuing wealth and luxury(奢侈) items before we realize this.

So what will bring us happiness? ___小题2:__ these three things have been proven by surveys of hundreds of thousands of people about what they have, what their lives are like, and how happy they are.

_____小题3:_____ We have a human need to be close to other human beings. Having good, supportive friendships, a strong marriage or close and loving relationships with our family members will make us much more likely to be happy. So take time to stay with your loved ones, to tell them what they mean to you, to listen to them.

Positive thinking can lead to happiness too. In fact, optimism and self-confidence are some of the indicators(迹象)of people who lead happy lives. So remember to get into the habit of squashing(排除)all negative thoughts and replacing them with positive ones.___小题4:____

The state we enter when we are completely focused on the work or task before us will almost undoubtedly lead to happiness. People find greatest enjoyment not when they are doing mindless work, but when they are absorbed in a mindful challenge.____小题5:_____ turn off the TV, get outside and do something that truly attract you.

You’ve been given the Three Secrets to Happiness. Don’t waste them.

A．Instead of “I can’t” think “I can”.

B．You will have good relationships with peoples around you.

C．But many times we act as if we’d be happier with a bit more money.

D．Luckily, it’s three things that don’t cost a thing.E.  Find work and hobbies that you’re passionate about seriously.

F.  The first thing is good relationships.

Most people value their personal happiness above money.

40臂井径仪一次下井可以获得套管最小内径和（）两条曲线。

A.外径

B.剩余壁厚

C.井温

D.磁定位

柴油机气阀阀杆的氮化处理，主要是为了提高阀杆抗腐蚀能力，而对阀杆的性能不会产生影响。（）