CSMA/CD

Question

Consider a scenario of CSMA / CD network. Suppose adapter A and B attempt to transmit a frame simultaneously and collide, with exponential back off algorithm.
A choose k =0 and B also choose k=0._Again they collide; after this collision both
A and B will choose k with equal probability from set A

(A) for A, {0,1} & for B, {0,1,2,3}

(B) for A , {0,1,2;3} &for B, {0,1,2,3}

(C) for A, {0,1} & for B, {0,1}

(D) None of these

Comments

after 1st collision $\left \{ 0,1 \right \}$

after 2nd collision $\left \{ 0,1,2,3 \right \}$

so B

Answer 1

in backoff algorithm

after 1st collission A & B will choose from range (0, $2^1$-1)

after 2nd collission A & B will choose from range (0,$2^2$-1) i.e from (0,1,2,3)  

so Answer is (B) for A , {0,1,2;3} &for B, {0,1,2,3}