Construct Finite Automata Whose Length Of String

Is Exact 2 Σ={a,b} // Input Alphabets   L={aa,ab,ba,bb} // Finite String

abc is invalid string // the length of abc is 3   {Q,Σ,δ,q0,F}   Q={q0,q1,q2,qd} Σ={a,b} q0={q0} F={q2}   (ab) // String   δ=(QXΣ->Q) δ(q0,a)->q1 δ(q1,b)->q2 δ(q0,a)->qd δ(q0,b)->qd δ(qd,a)->qd δ(qd,a)->qd    

b) at most 2 (Maximum 2)  // ('0','1','2')

L={ε,a,b,aa,ab,bb,ba}

        {Q,Σ,δ,q0,F}   Q={q0,q1,q2,qd} Σ={a,b} q0={q0} F={q0,q1,q2} δ=(QXΣ->Q)  

c) at least ' 2 ' // should be 2 and more than two

L={aa,ab,ba,bb,aba,bab......}   0,1 are rejected in this  

Example ababb(Valid String)