给出下面的代码段: public class Base{ int w,x,y,z; public Base(int a, int b){x=a; y=b;} public Base(int a, int b, int c, int d) { // assignment x=a,y=b w=d; z=c; } } 在代码说明// assignment x=a, y=b处写入如下哪几个代码是正确的? A. Base(a,b); B. x=a, y=b; C. x=a; y=b; D. this(a,b);