使用（）DPI的扫描分辨率扫描一幅6×8英寸的彩色图像，可以得到一幅1800×240

关于冬期施工混凝土的搅拌要求，下列说法不正确的是( )。

A．混凝土的搅拌时间比常温下要长

B．投放各种材料时，应先将水和砂石投入拌和后加入水泥

C．优先选用容量小的搅拌机，以加快搅拌速度，减少热量损失

D．混凝土搅拌前，先用热水或蒸汽冲洗搅拌机

阅读理解

     Scientist Florence Wambugu works with farmers in Kenya, a country in East Africa. She helps them

grow bigger and better crops. Wambugu is especially interested in finding simple ways to produce more

food.

     In the past ten years, Wambugu has spent much of her time studying sweet potatoes, which are an

important food in her part of Kenya. A virus (病毒) kept attacking the plants. It stopped the sweet

potatoes from growing well. Because of the virus, some farmers lost three quarters of their crops.

     Wambugu went to war against the virus. Her research for a way to save the sweet potatoes led to a

lab in St. Louis, Missouri.

     The lab mainly works on genes (基因), the chemical "computer programs" found in the cells of living

things. Genes tell a plant to produce pink flowers or an animal to grow black hair. Now scientists have

found ways to move genes from one living thing to another. That process is called genetic engineering.

     Wambugu spent three years in the lab. As a result, she created a sweet potato plant that could fight off

the virus. Wambugu tested her research in Kenya, and her plants produced wonderful sweet potatoes.

     That's just the beginning, Wambugu believes. Genetically modified (转基因的) foods, she thinks, could help farmers in poor countries grow badly needed crops, thus, fewer people will go hungry.

1. The text is written mainly to _______.

A. tell us sweet potatoes are in danger of being attacked by a virus

B. introduce Wambugu's contribution to genetic engineering

C. introduce a new way of killing plant viruses

D. tell how hard Wambugu worked in her lab for three years

2. What caused Wambugu to set up a lab in St. Louis, Missouri?

A. Her wish to save sweet potatoes in Kenya.

B. Her great interest in genetic engineering.

C. Her love for sweet potatoes.

D. Her interest in plant life.

3. The fourth paragraph mainly explains what ________ is.

A. a crop virus

B. chemical technology

C. a computer program

D. genetic engineering

4. What is Wambugu's attitude toward "genetic engineering"?

A. It will help more hungry people.

B. It should be carefully used.

C. It has more disadvantages than disadvantages.

D. It is a too expensive technology at present.

在线监测装置应能承受严酷等级为（）级的阻尼振荡磁场干扰。

A.5

B.6

C.7

D.8

阻抗的单位是（）。

A、亨利（H）

B、法拉（F）

C、瓦特（W）

D、欧姆（Ω）

简述ZK3-A型电空转机滑阀的工作原理。