诡异的静态构造函数

Question

public class Rational { protected static Rational one; public static Rational One { get { return one; } } protected static Rational zero; public static Rational Zero { get { return zero; } } { public int N { get; set; } public int M { get; set; } static Rational() { one = new Rational(1, 1); zero = new Rational(0, 1); } public Rational(int n, int m) { N = n; M = m; } public override string ToString() { return string.Format("{0}/{1}", N, M); } } static void Main(string[] args) {  Rational r1 = Rational.One;//r1 is 1/1 Rational r2 = Rational.Zero;//r2 is 0/1 Rational r = new Rational(1, 2);  Rational r3 = Rational.One;//r3 is 1/1  Rational r4 = Rational.Zero;//r4 is 0/1 } 但是: public class Ra { protected static Rational one; public static Rational One { get { return one; } } protected static Rational zero; public static Rational Zero { get { return zero; } } } public class Rational:Ra { public int N { get; set; } public int M { get; set; } static Rational() { one = new Rational(1, 1); zero = new Rational(0, 1); } public Rational(int n, int m) { N = n; M = m; } public override string ToString() { return string.Format("{0}/{1}", N, M); } }   static void Main(string[] args) {  Rational r1 = Rational.One;//r1 is null  Rational r2 = Rational.Zero;//r2 is null Rational r = new Rational(1, 2);  Rational r3 = Rational.One;//r3 is 1/1  Rational r4 = Rational.Zero;//r4 is 0/1 }字段在类中，静态构造函数会在第一次调用属性之前调用初始化静态字段，但是字段继承于基类，静态构造不会在调用属性之前初始为，而是在实例化类之后初始化，什么原因，什么解决办法？