Sparse population.
Fertile soil and abundant water resources.
The successful domestication.
Broad cultural interaction.
第1题:
The main propulsion diesel engine jacket water temperature rises above normal, with the raw sea suction and the expansion tank water level being normal. Which of the following problems is most likely the cause?
A.Faulty thermostatic bypass valve
B.Eroded zinc pencils in the heat exchanger
C.Steam formation in the expansion tank
D.Excessive leakage from jacket water pump seals
第2题:
Which of the following factors tends to increase scale formation on the saltwater side of a heat exchanger used in a diesel engine cooling water system?
A.Baffle plates that have been bent during prior removal
B.Leaks m the cooler tube nest
C.Operating the engine while maintaining a high sea water outlet temperature
D.A punctured sea water strainer supplying cooling water to the heat exchanger
第3题:
D
Have you ever noticed the colour of the water in a river or stream after a heavy rainfall? What do you think caused this change in colour? It is soil that has been washed into the river from the riverbank or from t}le nearby fields.
Components of Soil
Soil is made up of a number of layers(层),each having its own distinctive colour and texture. The upper layer is known as the litter. It acts like a blanket. limiting temperature changes and reducing water loss. The topsoil layer is made up of small particles of rock mixed with rotten plant and animal matter called humus(腐殖质),which is black and gives the topsoil its dark colour. This layer is usually rich in nutrients,oxygen,and water. Below the topsoil is the subsoil,a layer that contains more stones mixed with only small amounts of organic matter. This layer is lighter in colour because of the lack of humus. Beneath the soil lies a layer of bedrock.
Soil forms from the bottom up. Over time bedrock is attacked by rain, wind,frost, and snow. It is gradually broken down into smaller particles in a process called weathering. Plants begin to grow,and rotten materials enrich the topsoil. Most of the soil in Eastern Canada. for example. Was formed from weathered rock that was exposed when the ice disappeared l2,000 years ago.
Water Beneath the Soil
Surface water collects and flows above the ground in lakes. ponds. and rivers. Once in the soil or rock,it is called groundwater. Gravity pulls groundwater through the soil in a process called percolation(渗透). Eventually the water reaches a layer called the water table. Under this is bedrock through which water cannot percolate.
As water percolates downward,it dissolves organic matter and minerals from the soil and carries them to deeper layers. This causes a serious problem because plants require these nutrients for growth.
Soil pH
Soil can be acidic. neutral. or basic. The pH of the soil is determined by the nature of the rock
from which it was formed. and by the nature of the plants that grow and rot in it.
The acidity of rain and snow can lower the pH of the groundwater that enters the soil. By burning fossil fuels such as coal,oil and gasoline,humans have been contributing to higher levels of acidity in many soils. When fossil fuels are burned. gases are released into the air and then fall back to earth as acid rain. Acid soil increases出e problem of carrying nutrients to lower soil levels. As nutrients are removed,soil is less fertile. Plants grow more slowly in acidic soil,and also become easily attacked by diseases.
67. The layer of soil that provides necessary nutrients for plant growth is called.
A. 1itter B. topsoil C. humus D. subsoil
第4题:
第5题:
第6题:
Which of the following multicast mode does Auto-RP require?()
第7题:
3/4 percent American workers are potential applicants.
1.3 million jobs were created last year.
40 percent of companies will take on part-time staff.
The service sector does not contribute to job creation.
第8题:
Baffle plates that have been bent during prior removal
Leaks in the cooler tube nest
Operating the engine while maintaining a high sea water outlet temperature
A punctured sea water strainer supplying cooling water to the heat exchanger
第9题:
Feed-water heater internal tube surfaces
Internal distillate cooler tubes
Flash chamber vertical surfaces
Distilling condenser tubes
第10题:
AS path
Split horizon
Poison reverse
Unicast RPF check
第11题:
the transformation of these valleys and plains.
the use of these valleys’ soil and water.
the timing of flood seasons.
the calendar.
第12题:
第13题:
Which of the following conditions could contribute to the cracking of a diesel engine cylinder head?
A.Leaking seal ring
B.Insufficient heat transfer from the exhaust valves
C.Blocked cooling water passages to the head
D.Excessive scavenging air provided to the engine
第14题:
A. Link-mode
B. Dense mode
C. Sparse mode
D. Sparse-dense mode
第15题:
第16题:
第17题:
第18题:
Which multicast mode does Auto-RP require?()
第19题:
Leaking seal ring
Insufficient heat transfer from the exhaust valves
Block cooling water passages to the head
Excessive scavenging air provided to the engine
第20题:
(1)and(2)
(1)and(3)
(2)and(3)
(1),(2)and(3)
第21题:
Poor combustion
High cylinder oil consumption
Leaking exhaust valves
All of the above
第22题:
Avoidance.
Empathy.
Extroversion.
Introversion.
第23题:
Faulty thermostatic bypass valve
Eroded zinc pencils in the heat exchanger
Steam formation in the expansion tank
Excessive leakage from jacket water pump seal
第24题:
Sparse population.
Fertile soil and abundant water resources.
The successful domestication.
Broad cultural interaction.