问题 单项选择题 A1/A2型题

胎盘最重要的作用是()。

A.分泌孕激素和雌激素

B.分泌人绒毛膜促性腺激素

C.充当胎儿的肺

D.充当胎儿的内分泌器官

E.促进胎儿的血液循环

答案

参考答案:C

解析:胎盘最重要的作用是充当胎儿的肺。但气体交换的效率只有肺的1/50。母体血液输送氧至胎儿是在绒毛间隙弥散进入到胎儿血液循环的,而二氧化碳从胎儿血液循环向母体血液弥散,自高分压向低分压处弥散。母体若有严重肺炎、哮喘发作、充血性心力衰竭、抽搐时呼吸停止、麻醉对呼吸的抑制等均可使母体发生低氧血症而影响胎儿。

问答题
阅读理解

阅读理解。

     Most rain forests lie close to the equator (赤道), where the climate is often mild and there are long hours

of sunshine. The warmth of the land heats the air above, causing it to rise and tiny drops of water to fall as

rain. The rainfall can reach at least 98 inches a year. This wet, warm world with plenty of sunlight is perfect

for plants to grow, so the trees grow fast with green leaves all the year round. The trees themselves also hare

an effect on the climate. They gather water from the soil and pass it out into the air through their leaves. The

wet air then forms clouds, which hang over the treetops like smoke. These clouds protect the forest from the

daytime heat and night-time cold of nearby deserts, keep temperatures fit for plant growth.

     Rain forests slightly farther away from the equator remain just as warm, but they have a dry season of three

months or more when little rain falls, Tree leaves fall dining this dry season and new leaves grow when the wet

season or monsoon (雨季) begins Thus these areas are known as the "monsoon forest".

     Another type of rain forest grows on tropical mountains. It is often called the "cloud forest" because clouds

often hang over the trees like fog.

     The rain forest is the ideal place for the growth of many different trees. Most of them depend on animals to

eat their fruits and spread their seeds. When the fruits are eaten, the seeds inside them go undamaged through

animals, stomachs and are passed out in their droppings. The seeds lying on the forest floor then grow into

new trees.

1. The climate of the rain forests near the equator is _____.

A. mild, wet and windy

B. hot, rainy and foggy

C. hot, wet and cloudy

D. warm, wet and sunny

2. We can learn from the passage that _____.

A. tree leaves are green all the time in the monsoon forest

B. there is a dry season in the cloud forest on tropical mountains

C. clouds help the plants in the rain forest near the deserts to grow

D. the formation of climate in the rain forest has little to do with the trees

3. According to the passage _____ play the most important role in the spreading of seeds.

A. animals

B. droppings

C. fruits

D. winds

4. This passage is most likely to be found in _____.

A. a travel guide

B. a story book

C. a technical report

D. a geography book