Question from the C++ test

Consider class A, which defines a zero argument constructor and a one argument constructor which accepts an integer parameter.

Also class B is defined as

class B
{
        	public:
     	  
     	   explicit B(int)
         	{
     	   }
};
 
int main(int argc, char **argv)
{

Line number 1
A a1 = 77;
 
Line number 2
A a2;
 
Line number 3
A a3 = a1;
 
Line number 4
B b1 = 77;
 
Line number5
B b2(77);
 
return 0;
}