人体呼吸道具有净化空气的作用．下列能使吸入的气体变清洁的结构有（　　）

①鼻毛 ②声带 ③气管的内表面覆盖着有纤毛的黏膜 ④鼻黏膜  ⑤会厌软骨．

B

    Chris and Jessica live in Miami，Florida.They are packing(收拾行李)now.They're going away for a three-­week vacation tomorrow.They're going to rent(租)a house near a small lake about 100 miles north of the city.

    Chris is a carpenter(木匠)and he works hard.He often works ten hours a day，and he makes good money.He helps to build and repair houses.He likes his job and Miami.

    Jessica spends a lot of time working in her office and taking people to see houses.Her job and her family keep her busy.She gets little time to read and relax during the year.

    Chris and Jessica enjoy the quiet of the country.Chris loves fishing.He is going to rent a boat and he will go fishing on the lake for four or five hours every day during the vacation.

    Jessica doesn't like fishing，but she's an excellent swimmer.She is going swimming every afternoon during the vacation.After that，she will sit in the yard and read for a few hours.She especially likes to read novels.

Both Chris and Jessica believe that they will have a great time there!

根据下图数据判断，该图统计的是1895～1911年间中国（    ）

设e₁,e₂是夹角为45⁰的两个单位向量,且a=e₁+2e₂,b=2e₁+e₂,,则|a+b|的值     (    )