二尖瓣型心脏表现不包括（）. A.主动脉结缩小 B.肺动脉干凸出 C.左心室增大 D

约定真值可以通过（）途径获得。

A、校准

B、检定

C、多次测量

患者，女，38岁，右上25缺失，近远中间隙可，咬合正常。右上134牙体，牙周组织健康。右上6残冠，无松动，X线检查示已行根管治疗，根长度可。

左上6应采用的固位体是（）

A.全冠

B.3/4冠

C.嵌体

D.高嵌体

E.桩核冠

阅读理解。

     Planting trees around poultry (家禽) farms can improve air and water quality - and relations with

neighbors. Research has shown that just three rows of trees near poultry houses can reduce the release

of dust and ammonia (氨). They can also reduce the strong smell of ammonia gas.

     The trees capture dust, ammonia and smells in their leaves. They can also reduce energy use. They

also provide shade from the sun, so they reduce cooling costs in summer. And they act as a windbreak,

so they reduce heating costs in winter. Trees can also improve water quality around farms by removing

pollutions from soil and groundwater.

     Several years ago, people were objecting to the smell of poultry farms on the Delmarva Peninsula in

the eastern United States. Delmarva is where the states of Delaware, Maryland and Virginia come

together. Two thousand farms there can each house an average of seventy-five thousand chickens.

     Traditionally the farms used windows to provide fresh air in the chicken houses. Farmers rarely

planted trees or tall crops around the buildings, so there would be no barrier to the airflow.

     But then in the 60s, farms began to use mechanical ventilation (通风) systems. Instead of windows,

the mechanical systems used tunnel fans to circulate (使…循环) air. The fans directed airflow from the

poultry houses toward the homes of neighbors.

     Researchers began dealing with the problem in 2000. They found that over a period of six years,

planting three rows of trees reduced total dust and ammonia by more than half. And they found that

smells were reduced by 18%.

     Farmers may think trees will take too long to grow and be effective. But some trees can grow quickly. At least one-third of the Delmarva farms have planted trees, technically known as vegetative

environmental buffers. The idea offers a way to cut pollution, save money and energy, and make the

neighbors happy.

1. How did the mechanical ventilation system work?

_____________________________________________________

2. The number of chickens raised on the poultry farms in Delmarva is up to ____________________.

3. The benefits of planting trees around poultry farms are _________________.

4. What is the main topic of the passage?

_____________________________________________________

（）是木材最大的缺点。

A.易燃

B.易腐朽

C.易开裂和翘曲

D.易吸潮

现代医生的道德责任强调（）

A.对集体负责任

B.对患者负责任

C.对集体和社会负责任

D.对患者和社会负责任

E.对社会负责任