当肋间肌和隔肌收缩时，下列各项正确的是（　　）

①胸腔容积缩小；②胸腔容积扩大；③肺收缩；④肺扩张；⑤肺内气压低于大气压；⑥肺内气压高于大气压．

    Near the North Pole there are only two seasons: winter and summer. The winter Nights are long. For more than two months you can't see sun, ever at noon. The summer days are long.For more than two months the never sets and there is no night at all. The weather is cold all the year round. Even summer the temperatures below 0°C. So people there make their clothing with the fur of animals.

    In the cold climate, plants cannot grow. So people have to build their houses with fur, earth, shone or snow. When they go out hunting, they live in the tents of the fur. When they move, they take their tents with them. Sometimes, they build houses of snow. Now don't think that these houses must be cold, it is very warm and safe.

    The life near the North Polo is very interesting.

生活中遇到的问题，常常涉及化学知识，下列说法不正确的是（　　）