Which of the following statements are correct?

1. The signature of an indexer consists of the number and types of its formal parameters.
2. Indexers are similar to properties except that their accessors take parameters.
3. Accessors of interface indexers use modifiers.
4. The type of an indexer and the type of its parameters must be at least as accessible as the indexer itself.
5. An interface accessor contains a body.

1. A class
2. A property
3. A struct
4. A function
5. An interface

acc.accountNo = 10; 
Console.WriteLine(acc.accountNo);

Student s = new Student(); 
s[1, 2] = 35;

class Student
{ 
    int[ ] a = new int[5, 5]; 
    public property WriteOnly int this[int i, int j]
    { 
        set
        { 
            a[i, j] = value;
        } 
    }
}

class Student
{ 
    int[ , ] a = new int[5, 5]; 
    public int property WriteOnly
    { 
        set
        { 
            a[i, j] = value;
        } 
    } 
}

class Student
{ 
    int[ , ] a = new int[5, 5];
    public int this[int i, int j] 
    {
        set
        { 
            a[i, j] = value;
        } 
    } 
}

class Student
{ 
    int[ , ] a = new int[5, 5];
    int i, j; 
    public int this
    { 
        set
        { 
            a[i, j] = value;
        } 
    } 
}

Sample m = new Sample(); 
int l;
l = m.Length;

Sample m = new Sample(); 
m.Length = m.Length + 20;

Sample.Length = 20;

Console.WriteLine (Sample.Length);

Sample m = new Sample(); 
m.Length = 10;

Sample m = new Sample(); 
m.Length = 10;

Sample m = new Sample(); 
m.Length = m.Length + 20;

Sample m = new Sample(); 
int l;
l = m.Length;

Sample.Length = 20;

Console.WriteLine(Sample.Length);

1. Sample.Length = 20;

2. Sample m = new Sample(); 
   m.Length = 10;

3. Console.WriteLine(Sample.Length);

4. Sample m = new Sample(); 
   int len;
   len = m.Length;

5. Sample m = new Sample(); 
   m.Length = m.Length + 20;