For reaction $C+D\rightarrow A+B$,the rate expression is rate=$k[C]^{1/2}[D]^{1/2}$ starting with initial concentration of 4M of C and D each,what is time taken for concentration of A to become 0.25M.Given :$k=2.303\times 10^{-2}sec^{-1}$

Question

$(a)\;60sec\qquad(b)\;30sec\qquad(c)\;120sec\qquad(d)\;None$