玉米粗缩病是由玉米粗缩病病毒引起的一种病害，近年来该病的发生具有明显的上升趋势，对我国玉米生 产造成了极大的损失。 玉米粗缩病在玉米苗出土后即可发生，并在 5-6 片叶时才开始出现症状，感病
植株表现叶片宽短、僵直，叶色浓绿，顶叶簇生，成对生状。叶背面、叶脉上产生粗细不一的蜡白色条状 突起，有明显粗糙感。植株矮化，节间粗短。植株因感病时间不同，症状差异较大。一般感病越早，苗龄 越小，危害越
计算机能够处理数值、文字、声音、图像等信息，同学们可能会问：为什么 作为电子设备的计算机能处理那么多复杂的信息呢？实际上， 当把这些信息转换 成计算机能识别的形式就能进行处理。目前计算机中所有的信息都用“0”和 “1”两个数字符号组合的二进制数来表示。 数值、图形、文字等各种形式的信息，需要计算机加工处理时，首先必须按 一定的法则转换成二进制数。 然而，日常生活中使用的数是十进制数，它的特征是： （1）有 10 个数字：0、1、2、3、4、5、6、7、8、9。 （2）运算时逢十进一。 （3）每个数字在不同的数位上，其值的大小是不同的。 数位：个 十 百 千 万 …… 数值：100 101 102 103 104 …… 二进制数的特征是： （1）有 2 个数字：0，1。 （2）运算时逢二进一。 （3）每个数字在不同数位上，其值以 2 的倍数递增。即 20，21，22，23， 24，…… 用二进制数表示一个数值时,位数比较长，不便书写和记忆。由于又有下面 的关系：23=8 及 24=16，所以人们常用八进制数或十六进制数来表示二进制数。 八进制数的特征： （1）有八个数字：0，1，2，3，4，5，6，7。 （2）运算时逢八进一。 十六进制数的特征： （1）有十六个数字：0，1，2，3，4，5，6，7，8，9，A，B，C，D，E，F。
（2）运算时逢十六进一。 在十六进制中，分别用 A、B、C、D、E 和 F 来表示十进制数的 10、11、12、 13、14 和 15。 由此可得出：二进制、八进制、十进制与十六进制的特征对照表如表 2-2 所示。
表 2-2 二进制、八进制、十进制与十六进制的特征对照表
二进制数、八进制数、十进制数与十六进制数的对应关系表如表 2-3 所示。
表 2-3 二进制、八进制、十进制与十六进制的特征
我的好朋友 My Good FriendZhang Ying is my good friend. She’s in Class1, Grade4 of Tianjiao Primary School. She’s a model student. She’s clever and she’s helpful, too. She often helps teachers and young students at school. She is good at Chinese, maths, English, arts and crafts, music and so on. She has a lot of hobbies. She likes painting and drawing. And she likes listening to music, having picnics with her parents. Oh yeah, she likes fishing, too. But she doesn’t like playing basketball, football, table tennis or volleyball. Zhang Ying is the best friend of mine. I like playing with her. We always work together and help each other.
I have many friend.Do you know who they are?Are they my pet?No.Are they my classmates?No. Let me tell you:they are my favourit book. I like books very much.I like reading science book,cartoonbook so on.not only let me know how wonderful the word is but also teach me how to be a good person in the society,they give me great pleasure. I love books!
Lin Tao usually goes to the zoo with his parents. He likes to see animals. In his room there are many toys. Most of them are boy animals. All kinds of animals in his room are his good friend. Every day he plays with them.
Sometimes he asks his friends to his home to play. On vacation or weekends he like to see the monkeys and elephants in the zoo, and the dolphin show is his favorite.
我和我的朋友英语作文一：My Friend and Me
I met Chris in a calligraphy class last summer. He's my best bud. Chris is a tall guy and he likes playing basketball. I play basketball too but I'm not good at it at all. Calligraphy is our mutual hobby. We still go to the calligraphy class every Saturday morning. Sometimes we go to calligraphy exhibitions together. It's always nice to have such a good friend.
我和我的朋友英语作文二：My Friend and Me
My name is Wu Jie. I am a student of Dongzhou Middle School. I like playing basketball and singing. Zhang Jiong is my good friend. He wears a white T-shirt and blue jeans. He is very handsome. He likes playing football and singing. He is a good student. He usually helps me with my maths.
We are deskmates at school. On Sunday, we usually play football and swim together. We often visit each other and play computer games together. We are very happy to be with each other and help each other.
我和我的朋友英语作文三：My Friend and Me
Hello,everyone.I' m Sally.I have a friend.Her name is Amy.We are in the same class.She studys harder than me.I' m 160cm tall.She is 165cm.So she is taller than me.She likes darwing very much.I like taking photos.I' m 15 years old.But Amy is 16 years oid.So she is older than me.
What about you?And what about your friend?
我和我的朋友英语作文四：My Friend Hsiao-mei
Whenever I have a party, Hsiao-mei is always the first person I invite. She is such fun. I know that she will be able to make my other guests laugh. She does not get upset if somebody tries to tease or make fun of her, either. Hsiao-mei can also be very serious and can discuss almost anything you can think of. If it gets late before the party ends, I can always depend on Hsiao-mei to clean up the house. She never says no, even if she is very tired and would rather go straight home to bed.
我和我的朋友英语作文五： my friend and me
I have a friend.Her name is Nancy.She is from China.She is of medium biuld with long straight hair.She is very beautiful.My name is Tom.I also from China.China is a beautiful counthy with long history.I am tall,and I have short straight hair.My friend is friendly to me.And I also friendly to her.Sometimes,I play with her.We help each other.We are best friend!