Which of the following is correct way of concatenating two string objects in C++?way 1:string s1 = "hello";string s2 = "world";string s3 = s1 + s2;way 2:string s1 = "hello";string s2 = "world";string s3 = s1.append(s2);way 3:string s1 = "hello";string s2 = "world";string s3 = strcat(s1,s2);