问题 问答题 简答题

机械式换挡变速器有哪些功用和要求?

答案

参考答案:

功用:

1)变换档位;

2)变换方向;

3)挂空挡。

要求:

1)具体足够的档位与合适的传动比,使工程机械具有良好的牵引性、高的生产率及燃料使用经济性;

2)结构简单,传动效率高,工作可靠,使用寿命长,维修方便;

3)操纵轻便,不出现同时挂两个档、自行脱档和跳档等现象。

填空题
阅读理解

阅读理解。

     Three types of pangolins (穿山甲) exist in Africa - the giant pangolin, the tree pangolin and the most

widespread, the ground pangolin. Pangolins have small heads and long, broad tails. They are toothless and

have no external ears, although their hearing is good. Their sense of smell is well-developed, but their sight

is poor. The weight of the scales (鳞片) and skin make up about 20% of their weight.

     The common pangolin prefers sandy soils and is found in woodlands and savannas (热带草原), within

reach of water.

     All pangolins can roll themselves into a ball to defend themselves. The cutting action of their scales protects

them too. Pangolins also have scent glands (臭腺) that release strong, foul smelling secretions. Pangolins are

normally alone. Females are usually alone with their young. The young are 6 inches long and weigh 12 ounces

at birth. Their pale, soft scales begin to harden by the second day. The baby is folded in the mother's lap or

rolled-up body. It is nursed for 3 to 4 months and begins to eat termites (白蚁) at 1 month. At this time the

infant begins to accompany the mother, perhaps riding on the base of her tail. If the mother senses danger the

baby slips under her and is protected when she rolls up her body.

     Pangolins use their sense of smell to locate termite and ant nests. They dig up the insects with their claws

and use their extremely long tongues to eat them.

1. When pangolins are ____, they release strong, foul smelling secretions.

A. happy

B. sad

C. frightened

D. angry

2. Which of the following words best describes the function of the pangolin's scales? 

A. Heavy.

B. Beautiful.

C. Protective.

D. Hard.

3. When does the infant begin to accompany the mother pangolin?

A. At l month old.

B. At 2 months old.

C. At 2-3 months old.

D. At 3-4 months old.

4. What does the last paragraph mainly talk about?

A. The pangolin's habitat.

B. The pangolin's diet.

C. The pangolin's behavior.

D. The pangolin's appearance.