Which of the following are regular sets?

1. A.

   {anb2m|n≥0, m≥0}

2. B.

   {anbm | n = 2m}

3. C.

    {anbm n≠m}

4. D.

    {xcy | x,y ∈ {a,b}*}

Attempted by 91 students.