关于and和“，”连接句子的问题。

The traffic rule says young children（ under the age of four and____less than 40 pounds）
must be in a child safety seat.
从句中主语是
young children which is under the age of four and .weighing less than 40 pounds
主语是young children 和weigh存在主动关系，所以用ing和and没有关系，and只是连接句子，只是句子主语省略在前面。
D就是是非谓语动词
若是两句句子
l am a student，and he also is a student
连接两句句子，用（，and）。或者（;)或者直接（。）

克服思乡英语作文，题目是overcoming homesickness

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I left my home to go to a senior high school three years age, which is a boarding school far from my home. I was homesick at the beginning of the new school life. I missed my parents, my relatives, and my old friends at home. At the same time, I didn’t like the foods in the new school. As the result of this, I couldn’t help being absent-minded in classes. And I felt sick then. I even had the idea to quit school.
Meanwhile, I knew I have to overcome the homesickness and concentrate on my study. I began to make new friends and share their feelings. We studied and played together. After quite some time, I recovered gradually and went through the school life successfully.

2、定义一个学生类Student,它继承自person类。

不知道要那个toString()方法有什么用，回去好好看看方法的重写和重载去，总是看你提问题了，怎么老不会做呢！郁闷！下次自己写！ //父类 public class person { String name; String sex; int age; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String toString(){ return null; } public person(String name, String sex, int age) { this.name = name; this.sex = sex; this.age = age; } } //子类 public class Student extends person { long number; int phi; int eng; int comp; public long getNumber() { return number; } public void setNumber(long number) { this.number = number; } public int getPhi() { return phi; } public void setPhi(int phi) { this.phi = phi; } public int getEng() { return eng; } public void setEng(int eng) { this.eng = eng; } public int getComp() { return comp; } public void setComp(int comp) { this.comp = comp; } public Student(String name, String sex, int age, long number, int phi, int eng, int comp) { super(name, sex, age); this.number = number; this.phi = phi; this.eng = eng; this.comp = comp; } public double aver(){ return (phi eng comp)/3; } public int max(){ return Math.max(Math.max(phi, eng), comp); } public int min(){ return Math.min(Math.min(phi, eng), comp); } public String toString(){ return null; } } //测试程序 public class test { public static void main(String args[]){ Student s = new Student("李丽","女",18,200501,80,95,85); System.out.print("学号：" s.getNumber()); System.out.print("姓名：" s.getName()); System.out.print("性别：" s.getSex()); System.out.print("年龄：" s.getAge()); System.out.print("平均分：" s.aver()); System.out.print("最高分：" s.max()); System.out.print("最低分：" s.min()); } }