问题 选择题

根尖的成熟区是植物吸收水分的主要部位,其主要原因是(  )

A.成熟区位于根尖的顶端

B.成熟区的细胞形似正方形

C.成熟区有大量的根毛

D.成熟区的细胞体积很小

答案

根尖是指从根的顶端到生有根毛的一段.它的结构从顶端依次是根冠、分生区、伸长区、成熟区.成熟区也叫根毛区,表皮细胞一部分向外突起形成根毛.是吸收水分和无机盐的主要部位.根毛的存在增加了根的吸收面积.根毛能分泌多种物质,如有机酸等,使土壤中难于溶解的盐类溶解,成为容易被植物吸收的养分.成熟区及其上部,根内部一部分细胞分化形成导管,能输导水分和无机盐.

故答案为:C.

阅读理解

阅读理解。

     High school students in America hear about twenty bells every day. The first bell is the tardy bell(上课铃) .If students are not in their seats when the tardy bell rings,they know they are late. Another bell rings at the end of each class,and everyone leaves class quickly and goes to the next class. When students are in a hard class,they are often happy to hear the bell ring. If the class is interesting(右趣的) ,they do not want

the bell to ring.Most students like the lunch bell best. They know that it is time to join(参加) their friends

for lunch. They buy a hot meal in the school dining hall or they bring their lunch from home in a big paper

bag, After a nice lunch,everyone knows that it is soon time for another bell,another bell,another bell.

1. American students in high school hear about               bells every day.

A. many

B. twenty

C. twelve

D. much

2. The students know they are late if they               .

A. don't come to school early

B. are not in their seats when they hear the first bell

C. hear another bell in the classroom

D. are in their seats before the first bell rings

3. The students are happy to have               .

A. interesting classes

B. a hard class

C. all the classes

D. a difficult class

4. Why do most students like the lunch bell best? Because               .

A. they don't like their classes at all

B. they can enjoy(享用)their meals

C. they can join their friends for lunch

D. they can have a lot of food to eat

5. The students usually have their lunch                 .

A. at school

B. in the restaurant

C. at home

D. at the party

单项选择题