Which among the following is correct?

• A. class student{ }s1,s2; s1.student()=s2.student();
• B. class student{ }s1; class topper{ }t1; s1=t1;
• C. class student{ }s1,s2; s1=s2;
• D. Class student{ }s1; class topper{ }t1; s1.student()=s2.topper();